The growing demand for high-power-density electric and electronic systems has encouraged the development of energy-storage capacitors with attributes such as high energy density,high capacitance density,high voltage a...The growing demand for high-power-density electric and electronic systems has encouraged the development of energy-storage capacitors with attributes such as high energy density,high capacitance density,high voltage and frequency,low weight,high-temperature operability,and environmental friendliness.Compared with their electrolytic and film counterparts,energy-storage multilayer ceramic capacitors(MLCCs)stand out for their extremely low equivalent series resistance and equivalent series inductance,high current handling capability,and high-temperature stability.These characteristics are important for applications including fast-switching third-generation wide-bandgap semiconductors in electric vehicles,5G base stations,clean energy generation,and smart grids.There have been numerous reports on state-of-the-art MLCC energy-storage solutions.However,lead-free capacitors generally have a low-energy density,and high-energy density capacitors frequently contain lead,which is a key issue that hinders their broad application.In this review,we present perspectives and challenges for lead-free energy-storage MLCCs.Initially,the energy-storage mechanism and device characterization are introduced;then,dielectric ceramics for energy-storage applications with aspects of composition and structural optimization are summarized.Progress on state-of-the-art energy-storage MLCCs is discussed after elaboration of the fabrication process and structural design of the electrode.Emerging applications of energy-storage MLCCs are then discussed in terms of advanced pulsed power sources and high-density power converters from a theoretical and technological point of view.Finally,the challenges and future prospects for industrialization of lab-scale lead-free energy-storage MLCCs are discussed.展开更多
Relaxor dielectric ceramic capacitors are very attractive for high-power energy storage.However,the low breakdown strength severely restricts improvements to the energy storage density and practical application.Here,a...Relaxor dielectric ceramic capacitors are very attractive for high-power energy storage.However,the low breakdown strength severely restricts improvements to the energy storage density and practical application.Here,a strategy of designing small grain sizes and abundant amorphous grain boundaries is proposed to improve the energy storage properties under the guidance of phase field theory.0.925(K_(0.5)Na_(0.5))NbO_(3)-e0.075Bi(Zn_(2/3)(Ta_(0.5)Nb_(0.5))1/3)O_(3)(KNNe-BZTN)relaxor ferroelectric ceramic is taken as an example to verify our strategy.The grain sizes and grain boundaries of the KNNeBZTN ceramics are carefully controlled by the high-energy ball milling method and twoestep sintering strategy.Impedance analysis and diffusion reflectance spectra demonstrate that KNNeBZTN ceramics with a small grain size and abundant amorphous grain boundary exhibit a lower charge carrier concentration and higher band gap.As a consequence,the breakdown electric field of KNNeBZTN ceramics increases from 222 kV/cm to 317 kV/cm when the grain size is decreased from 410 nm to 200 nm,accompanied by a slightly degraded maximum polarization.KNNeBZTN ceramics with an average grain size of~250 nm and abundant amorphous grain boundaries exhibit optimum energy storage properties with a high recoverable energy density of 4.02 J/cm^(3) and a high energy efficiency of 87.4%.This successful local structural design opens up a new paradigm to improve the energy storage performance of other dielectric ceramic capacitors for electrical energy storage.展开更多
Local electric-field around multitype pores(dielectric pore,interface pore,electrode pore)in multilayer ceramic capacitors(MLCCs)was investigated using Kelvin probe force microscopy combined with the finite element si...Local electric-field around multitype pores(dielectric pore,interface pore,electrode pore)in multilayer ceramic capacitors(MLCCs)was investigated using Kelvin probe force microscopy combined with the finite element simulation to understand the effect of pores on the electric reliability of MLCCs.Electricfield is found to be concentrated significantly in the vicinity of these pores and the strength of the local electric-field is 1.5e5.0 times of the nominal strength.Unexpectedly,the concentration degree of the pores in the inner electrode is much higher than that in the dielectrics and dielectric-electrode interfaces.Meanwhile,geometry orientations are found to have a remarkable influence on the local electric field strength.The pores act as an insulation degradation precursor via local electric,thermal center,and oxygen vacancies accumulation center.Such unusual local electric field concentration of multitype pores can provide new insights into the understanding of insulation degradation evolution,processing tailoring and design optimization for MLCCs.展开更多
We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two- dimensional （2D） photonic crystal （PhC） slabs by expanding the electromagnetic field on the basis of waveguide mode...We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two- dimensional （2D） photonic crystal （PhC） slabs by expanding the electromagnetic field on the basis of waveguide modes of an effective homogeneous waveguide. The introduction of the third component into the 2D PhC slabs influences the photonic band structure and the intrinsic losses of the system. We examine the dependences of the band gap width and gap edge position on the interlayer dielectric constant and interlayer thickness. It is found that the gap edges shift to lower frequencies and the intrinsic losses of each band decrease with the increasing interlayer thickness or dielectric constant. During the design of the real PhC system, the effect of unintentional native oxide surface layer on the optical properties of 2D PhC slabs has to be taken into consideration. At the same time, intentional oxidization of macroporous PhC structure can be utilized to optimize the design.展开更多
The electrocaloric effect(ECE) of multilayer ceramic capacitor(MLCC) of Y5 V type was directly measured via a differential scanning calorimetry(DSC) method and a reference resistor was used to calibrate the heat flow ...The electrocaloric effect(ECE) of multilayer ceramic capacitor(MLCC) of Y5 V type was directly measured via a differential scanning calorimetry(DSC) method and a reference resistor was used to calibrate the heat flow due to the heat dissipation. The results are compared with those calculated from Maxwell relations by using the polarization data obtained from the polarization–electric field hysteresis loops. The direct method shows a larger ECE temperature change, which is accounted for the situation approaches an ideal condition. For the indirect method using Maxwell relations, only the polarization projection along the electric field was taken into account, which will be less than the randomly distributed real polarizations that contribute to the ECE. The MLCCs exhibit a broad peak of ECE around 80 C, which will be favorite for the practical ECE cooling devices.展开更多
A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors （MLCC）. Spherical ultrafine cuprous oxide （Cu20） powder was prepared by glucose reduction of Cu（OH）2. The Cu20 p...A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors （MLCC）. Spherical ultrafine cuprous oxide （Cu20） powder was prepared by glucose reduction of Cu（OH）2. The Cu20 particles were coated by Mg（OH）2 and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, tap density, and thermogravimetry （TG）. It is found that the shape and size distribution of the copper powder are determined by the Cu20 powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg（OH）2 coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm3 and the initial oxidation temperature rises from 125 to 150~C.展开更多
Although dielectric ceramic capacitors possess attractive properties for high-power energy storage,their pronounced electrostriction effect and high brittleness are conducive to easy initiation and propagation of crac...Although dielectric ceramic capacitors possess attractive properties for high-power energy storage,their pronounced electrostriction effect and high brittleness are conducive to easy initiation and propagation of cracks that significantly deteriorate electrical reliability and lifetime of capacitors in practical applications.Herein,a new strategy for designing relaxor ferroelectric ceramics with K_(0.5)Na_(0.5)NbO_(3)-core/SiO_(2)-shell structured grains was proposed to simultaneously reduce the electric-field-induced strain and enhance the mechanical strength of the ceramics.The simulation and experiment declared that the bending strength and compression strength of the core-shell structured ceramic were shown to increase by more than 50% over those of the uncoated sample.Meanwhile,the electric-field-induced strain was reduced by almost half after adding the SiO_(2) coating.The suppressed electrical deformation and enhanced mechanical strength could alleviate the probability of generation of cracks and prevent their propagation,thus remarkably improving breakdown strength and fatigue endurance of the ceramics.As a result,an ultra-high breakdown strength of 425 kV cm^(-1) and excellent recoverable energy storage density(Wrec~4.64 J cm^(-3))were achieved in the core-shell structured sample.More importantly,the unique structure could enhance the cycling stability of the ceramic(Wrec variation<±2% after 105 cycles).Thus,mechanical performance optimization via grain structure engineering offers a new paradigm for improving electrical breakdown strength and fatigue endurance of dielectric ceramic capacitors.展开更多
基金supported by National Key R&D Program of China(No.2017YFB0406302)Key-Area Research and Development Program of Guangdong Province(No.2019B090912003)+2 种基金the National Natural Science Foundation of China(No.52002253)Sichuan Science and Technology Program(No.2021YFH0181)Shuimu Tsinghua Scholar Program,and State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KFZD202002).
文摘The growing demand for high-power-density electric and electronic systems has encouraged the development of energy-storage capacitors with attributes such as high energy density,high capacitance density,high voltage and frequency,low weight,high-temperature operability,and environmental friendliness.Compared with their electrolytic and film counterparts,energy-storage multilayer ceramic capacitors(MLCCs)stand out for their extremely low equivalent series resistance and equivalent series inductance,high current handling capability,and high-temperature stability.These characteristics are important for applications including fast-switching third-generation wide-bandgap semiconductors in electric vehicles,5G base stations,clean energy generation,and smart grids.There have been numerous reports on state-of-the-art MLCC energy-storage solutions.However,lead-free capacitors generally have a low-energy density,and high-energy density capacitors frequently contain lead,which is a key issue that hinders their broad application.In this review,we present perspectives and challenges for lead-free energy-storage MLCCs.Initially,the energy-storage mechanism and device characterization are introduced;then,dielectric ceramics for energy-storage applications with aspects of composition and structural optimization are summarized.Progress on state-of-the-art energy-storage MLCCs is discussed after elaboration of the fabrication process and structural design of the electrode.Emerging applications of energy-storage MLCCs are then discussed in terms of advanced pulsed power sources and high-density power converters from a theoretical and technological point of view.Finally,the challenges and future prospects for industrialization of lab-scale lead-free energy-storage MLCCs are discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.52072150,51702119,51702122,51972146)Young Elite Scientists Sponsorship Program by CAST.
文摘Relaxor dielectric ceramic capacitors are very attractive for high-power energy storage.However,the low breakdown strength severely restricts improvements to the energy storage density and practical application.Here,a strategy of designing small grain sizes and abundant amorphous grain boundaries is proposed to improve the energy storage properties under the guidance of phase field theory.0.925(K_(0.5)Na_(0.5))NbO_(3)-e0.075Bi(Zn_(2/3)(Ta_(0.5)Nb_(0.5))1/3)O_(3)(KNNe-BZTN)relaxor ferroelectric ceramic is taken as an example to verify our strategy.The grain sizes and grain boundaries of the KNNeBZTN ceramics are carefully controlled by the high-energy ball milling method and twoestep sintering strategy.Impedance analysis and diffusion reflectance spectra demonstrate that KNNeBZTN ceramics with a small grain size and abundant amorphous grain boundary exhibit a lower charge carrier concentration and higher band gap.As a consequence,the breakdown electric field of KNNeBZTN ceramics increases from 222 kV/cm to 317 kV/cm when the grain size is decreased from 410 nm to 200 nm,accompanied by a slightly degraded maximum polarization.KNNeBZTN ceramics with an average grain size of~250 nm and abundant amorphous grain boundaries exhibit optimum energy storage properties with a high recoverable energy density of 4.02 J/cm^(3) and a high energy efficiency of 87.4%.This successful local structural design opens up a new paradigm to improve the energy storage performance of other dielectric ceramic capacitors for electrical energy storage.
基金supported by the National Key R&D Program of China(No.2021YFB3800604 and No.2021YFA0716502)Shanghai Pilot Program for Basic Research-Chinese Academy of Science Shanghai Branch(JCYJ-SHFY-2022-002)+1 种基金the Instrument Developing Project of Chinese Academy of Sciences(No.ZDKYYQ20180004)the Shanghai Sailing Program(No.20YF1455600)and Hengdian Group Holding Co.LTD。
文摘Local electric-field around multitype pores(dielectric pore,interface pore,electrode pore)in multilayer ceramic capacitors(MLCCs)was investigated using Kelvin probe force microscopy combined with the finite element simulation to understand the effect of pores on the electric reliability of MLCCs.Electricfield is found to be concentrated significantly in the vicinity of these pores and the strength of the local electric-field is 1.5e5.0 times of the nominal strength.Unexpectedly,the concentration degree of the pores in the inner electrode is much higher than that in the dielectrics and dielectric-electrode interfaces.Meanwhile,geometry orientations are found to have a remarkable influence on the local electric field strength.The pores act as an insulation degradation precursor via local electric,thermal center,and oxygen vacancies accumulation center.Such unusual local electric field concentration of multitype pores can provide new insights into the understanding of insulation degradation evolution,processing tailoring and design optimization for MLCCs.
基金supported in part by the National Natural Science Foundation of China (No. 60707001,60711140087)the National "973" Program of China(No. 2007CB310705)+4 种基金the National "863" Program of China (No. 2007AA01Z247)NCET (07-0110)PCSIRT(No. IRT0609)ISTCP (No. 2006DFA11040)P. R.China
文摘We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two- dimensional （2D） photonic crystal （PhC） slabs by expanding the electromagnetic field on the basis of waveguide modes of an effective homogeneous waveguide. The introduction of the third component into the 2D PhC slabs influences the photonic band structure and the intrinsic losses of the system. We examine the dependences of the band gap width and gap edge position on the interlayer dielectric constant and interlayer thickness. It is found that the gap edges shift to lower frequencies and the intrinsic losses of each band decrease with the increasing interlayer thickness or dielectric constant. During the design of the real PhC system, the effect of unintentional native oxide surface layer on the optical properties of 2D PhC slabs has to be taken into consideration. At the same time, intentional oxidization of macroporous PhC structure can be utilized to optimize the design.
基金supported by the National Natural Science Foundation of China(Grant No.51372042)the Department of Education of Guangdong Province of People’s Republic of China(Grant No.2014GKXM039)+1 种基金Guangdong Provincial Natural Science Foundation(Grant No.2015A030308004)the NSFC-Guangdong Joint Fund(Grant NoU1501246)
文摘The electrocaloric effect(ECE) of multilayer ceramic capacitor(MLCC) of Y5 V type was directly measured via a differential scanning calorimetry(DSC) method and a reference resistor was used to calibrate the heat flow due to the heat dissipation. The results are compared with those calculated from Maxwell relations by using the polarization data obtained from the polarization–electric field hysteresis loops. The direct method shows a larger ECE temperature change, which is accounted for the situation approaches an ideal condition. For the indirect method using Maxwell relations, only the polarization projection along the electric field was taken into account, which will be less than the randomly distributed real polarizations that contribute to the ECE. The MLCCs exhibit a broad peak of ECE around 80 C, which will be favorite for the practical ECE cooling devices.
文摘A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors （MLCC）. Spherical ultrafine cuprous oxide （Cu20） powder was prepared by glucose reduction of Cu（OH）2. The Cu20 particles were coated by Mg（OH）2 and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, tap density, and thermogravimetry （TG）. It is found that the shape and size distribution of the copper powder are determined by the Cu20 powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg（OH）2 coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm3 and the initial oxidation temperature rises from 125 to 150~C.
基金This work was supported by the National Natural Science Foundation of China(grants nos.52072150,51972146,and 51772175)the China Association for Science and Technology(Young Elite Scientists Sponsorship Program)the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(project no.KF202002).
文摘Although dielectric ceramic capacitors possess attractive properties for high-power energy storage,their pronounced electrostriction effect and high brittleness are conducive to easy initiation and propagation of cracks that significantly deteriorate electrical reliability and lifetime of capacitors in practical applications.Herein,a new strategy for designing relaxor ferroelectric ceramics with K_(0.5)Na_(0.5)NbO_(3)-core/SiO_(2)-shell structured grains was proposed to simultaneously reduce the electric-field-induced strain and enhance the mechanical strength of the ceramics.The simulation and experiment declared that the bending strength and compression strength of the core-shell structured ceramic were shown to increase by more than 50% over those of the uncoated sample.Meanwhile,the electric-field-induced strain was reduced by almost half after adding the SiO_(2) coating.The suppressed electrical deformation and enhanced mechanical strength could alleviate the probability of generation of cracks and prevent their propagation,thus remarkably improving breakdown strength and fatigue endurance of the ceramics.As a result,an ultra-high breakdown strength of 425 kV cm^(-1) and excellent recoverable energy storage density(Wrec~4.64 J cm^(-3))were achieved in the core-shell structured sample.More importantly,the unique structure could enhance the cycling stability of the ceramic(Wrec variation<±2% after 105 cycles).Thus,mechanical performance optimization via grain structure engineering offers a new paradigm for improving electrical breakdown strength and fatigue endurance of dielectric ceramic capacitors.
