Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in stu...Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.展开更多
Dielectric polymers are the materials of choice for high energy density film capacitors.The increasing demand for advanced electrical systems requires dielectric polymers to operate efficiently under extreme condition...Dielectric polymers are the materials of choice for high energy density film capacitors.The increasing demand for advanced electrical systems requires dielectric polymers to operate efficiently under extreme conditions,especially at elevated temperatures.However,the low permittivity and relatively low operating temperature of dielectric polymers limit the high-temperature capacitive energy storage applications.Fortunately,dipolar glass polymers are demonstrated as the preferred materials to achieve high dielectric constant,low dielectric loss and high energy density at elevated temperatures.In this review,we critically elaborate on the recent progress of dipolar glass polymers based on orientational polarization from molecular engineering.In addition,the general design considerations and various dipole moment entities of dipolar glass polymers are described in detail.High dipolar moment,high dipole density and rotation freedom of dipoles are essential for dipolar glass polymers to gain superior dielectric and energy storage properties.Challenges and future opportunities for dipolar glass polymers towards high-temperature energy storage applications are also provided.展开更多
High-entropy materials are highly attractive due to their unique structural characteristics and exceptional properties which find various promising applications such as energy technology,electronics,catalysis,and biom...High-entropy materials are highly attractive due to their unique structural characteristics and exceptional properties which find various promising applications such as energy technology,electronics,catalysis,and biomedicine[1–3].Current highentropy materials essentially involve alloys and ceramics,while“high-entropy polymers have been rarely reported”[4],as commented by Prof.Yeh JW who coined the term of highentropy alloys in 2004[1].展开更多
Dielectric materials with enhanced energy storage performances are urgently demanded owing to the development of advanced capacitor equipment.However,low energy density and weak self-healing capabilities of current di...Dielectric materials with enhanced energy storage performances are urgently demanded owing to the development of advanced capacitor equipment.However,low energy density and weak self-healing capabilities of current dielectric materials still limit the practical applications.Here,a biaxially oriented(polypropylene/two-dimensional(2D)Al_(2)O_(3) nanosheets/grafted polypropylene)nanocomposite was proposed.The biaxial orientation enabled the directional arrangement of nanosheets in the polymer matrix.The oriented 2D nanosheets played a dominate role in the restriction of charge transportation and the tradeoff of energy consumption during breakdown and self-healing.Therefore,on one hand,the discharge energy density reached a considerable value of 9.64 J/cm^(3).On the other hand,the self-healing area of the metalized films was a 36% smaller than that of biaxially oriented polypropylene(BOPP)at the comparable self-healing energy,which was related to the long-term reliability of capacitor.The further experiments and simulations indicated that the oriented γ-A_(2)O_(3) nanosheets(AONs)arrangement suppressed electric field distortion and hindered the charge transportation,which greatly enhanced the breakdown strength and ultimately improved the energy storage performance.This strategy presented a potential solution for improving the energy storage performance of capacitor films,which is suitable for current industrial production.展开更多
Biaxially oriented polypropylene(BOPP)thin film is the predominant dielectric material used in film capacitive energy storage for pulsed power engineering and power conver-sions due to its remarkable high dielectric s...Biaxially oriented polypropylene(BOPP)thin film is the predominant dielectric material used in film capacitive energy storage for pulsed power engineering and power conver-sions due to its remarkable high dielectric strength and low conduction loss.However,the design rating of BOPP film capacitors in high power density conversion systems operated also under high temperature is still based on the empirical criteria due to the lack of systematic mechanism studies at elevated temperature.In this work,the temperature-dependent electrical conduction in tenter and bubble BOPP films up to their break-down strength was systematically studied using a specialised circuitry featuring dynamic gain-controlled capacitive current cancellation.Both tenter and bubble BOPP films exhibit an extended trap-limited conduction region at the high electric field,followed subsequently with a trap-filled limited conduction until breakdown.This trap-filled-limited conduction presents characteristics of carriers transport with detrimental high mobility and soaring conduction loss.Overall,the shallow localised states revealed by the Arrhenius analysis,the large bandgap,and high barrier height of BOPP film together render its exceptional electrical integrity.In comparison,the enhanced crystallinity and larger crystallite sizes in tenter BOPP produced by the sequential stretching result in a higher upper operational temperature and slightly higher breakdown strength than bubble BOPP,suggesting the important role of processing induced enhancements to intrinsic properties of molecular origin.This study provides insights into the high-field charac-teristics of BOPP films at elevated temperature with promising learning outcomes useful to the expedited designs of the next generation polymer films for capacitive energy storages.展开更多
基金financial support from the National Science Foundation of China(22078190)the National Key R&D Plan of China(2020YFB1505802)。
文摘Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.
基金financially supported by the National Natural Science Foundation of China(Nos.51973080,92066104 and 51903100)。
文摘Dielectric polymers are the materials of choice for high energy density film capacitors.The increasing demand for advanced electrical systems requires dielectric polymers to operate efficiently under extreme conditions,especially at elevated temperatures.However,the low permittivity and relatively low operating temperature of dielectric polymers limit the high-temperature capacitive energy storage applications.Fortunately,dipolar glass polymers are demonstrated as the preferred materials to achieve high dielectric constant,low dielectric loss and high energy density at elevated temperatures.In this review,we critically elaborate on the recent progress of dipolar glass polymers based on orientational polarization from molecular engineering.In addition,the general design considerations and various dipole moment entities of dipolar glass polymers are described in detail.High dipolar moment,high dipole density and rotation freedom of dipoles are essential for dipolar glass polymers to gain superior dielectric and energy storage properties.Challenges and future opportunities for dipolar glass polymers towards high-temperature energy storage applications are also provided.
文摘High-entropy materials are highly attractive due to their unique structural characteristics and exceptional properties which find various promising applications such as energy technology,electronics,catalysis,and biomedicine[1–3].Current highentropy materials essentially involve alloys and ceramics,while“high-entropy polymers have been rarely reported”[4],as commented by Prof.Yeh JW who coined the term of highentropy alloys in 2004[1].
基金Project supported by the National Natural Science Foundation of China(No.U24A20151)。
文摘Dielectric materials with enhanced energy storage performances are urgently demanded owing to the development of advanced capacitor equipment.However,low energy density and weak self-healing capabilities of current dielectric materials still limit the practical applications.Here,a biaxially oriented(polypropylene/two-dimensional(2D)Al_(2)O_(3) nanosheets/grafted polypropylene)nanocomposite was proposed.The biaxial orientation enabled the directional arrangement of nanosheets in the polymer matrix.The oriented 2D nanosheets played a dominate role in the restriction of charge transportation and the tradeoff of energy consumption during breakdown and self-healing.Therefore,on one hand,the discharge energy density reached a considerable value of 9.64 J/cm^(3).On the other hand,the self-healing area of the metalized films was a 36% smaller than that of biaxially oriented polypropylene(BOPP)at the comparable self-healing energy,which was related to the long-term reliability of capacitor.The further experiments and simulations indicated that the oriented γ-A_(2)O_(3) nanosheets(AONs)arrangement suppressed electric field distortion and hindered the charge transportation,which greatly enhanced the breakdown strength and ultimately improved the energy storage performance.This strategy presented a potential solution for improving the energy storage performance of capacitor films,which is suitable for current industrial production.
基金Office of Naval Research,Grant/Award Numbers:N00014-17-1-2656,N00014-23-1-2292,N00014-23-1-2346,N00014-23-1-2348。
文摘Biaxially oriented polypropylene(BOPP)thin film is the predominant dielectric material used in film capacitive energy storage for pulsed power engineering and power conver-sions due to its remarkable high dielectric strength and low conduction loss.However,the design rating of BOPP film capacitors in high power density conversion systems operated also under high temperature is still based on the empirical criteria due to the lack of systematic mechanism studies at elevated temperature.In this work,the temperature-dependent electrical conduction in tenter and bubble BOPP films up to their break-down strength was systematically studied using a specialised circuitry featuring dynamic gain-controlled capacitive current cancellation.Both tenter and bubble BOPP films exhibit an extended trap-limited conduction region at the high electric field,followed subsequently with a trap-filled limited conduction until breakdown.This trap-filled-limited conduction presents characteristics of carriers transport with detrimental high mobility and soaring conduction loss.Overall,the shallow localised states revealed by the Arrhenius analysis,the large bandgap,and high barrier height of BOPP film together render its exceptional electrical integrity.In comparison,the enhanced crystallinity and larger crystallite sizes in tenter BOPP produced by the sequential stretching result in a higher upper operational temperature and slightly higher breakdown strength than bubble BOPP,suggesting the important role of processing induced enhancements to intrinsic properties of molecular origin.This study provides insights into the high-field charac-teristics of BOPP films at elevated temperature with promising learning outcomes useful to the expedited designs of the next generation polymer films for capacitive energy storages.
