In this work, exhaustive characterizations of 3D geometries of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and NMC/LFP blended electrodes are undertaken for rational interpretation of their measured ...electrical properties and electrochemical performance. X‐ray tomography and focused ion beam in combination with scanning electron microscopy tomography are used for a multiscale analysis of electrodes 3D geometries. Their multiscale electrical properties are measured by using broadband dielectric spectroscopy. Finally, discharge rate performance are measured and analyzed by simple, yet efficient methods. It allows us to discriminate between electronic and ionic wirings as the performance limiting factors, depending on the discharge rate. This approach is a unique exhaustive analysis of the experimental relationships between the electrochemical behavior, the transport properties within the electrode, and its 3D geometry.
Multiscale characterizations of 3D geometries and electrical properties of Li‐ion electrodes made of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and NMC/LFP blend allow the rational interpretation of their electrochemical performance by discriminating between electronic and ionic wirings as the performance limiting factors, depending on the discharge rate.
Glass fiber (GF) reinforced polymer composites have attracted increasing attention due to their excellent performance. In this study, GF was coated by a thin layer of nickel, and then grafted carbon ...nanotubes (CNTs) array by a chemical vapor deposition method (CVD). The CNT contents can be varied by changing the CVD conditions. Three types of fillers, nickel coated GF (GF@Ni), GF with CVD grown CNTs (GF-CNTs) and nickel-coated GF with CVD grown CNTs (GF@Ni-CNTs), were used to prepare the epoxy composites. The electromagnetic interference shielding performances were investigated as a function of CNT contents. The GF@Ni-CNTs reinforced epoxy composites, which had the CNTs mass ratio of 9.2 wt% to the hybrids, showed the best EMI shielding performance among the composites. Their total EMI shielding effectiveness (SE) was higher than 35 dB in the range of 1–18 GHz, and above 50 dB in the X band. By incorporating the nickel layer on the GF surface, the same EMI performance can be achieved with lower CNTs content. For achieving a SE value of 35 dB in the X band, it needed GF@Ni-CNTs/epoxy with CNTs mass ratio of 3.8 wt% to the hybrids, instead of GF-CNTs/epoxy composites with CNTs mass ratio of 5.2 wt% to the hybrids.
The broadband dielectric spectroscopy technique is applied, for the first time, to a composite material used as an electrode for lithium battery. The electrical properties (permittivity and ...conductivity) are measured from low (a few Hz) to microwave (a few GHz) frequencies. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. This work opens up new prospects for a more fundamental understanding and more rational optimization of the electronic transport in composite electrodes for lithium batteries and other electrochemical energy storage technologies (including other batteries, supercapacitors, low‐ and medium‐temperature fuel cells), electrochemical sensors and conductor–insulator composite materials.
A lithium battery electrode is characterized using the broadband dielectric spectros copy technique. From interatomic distances to macroscopic sizes, the technique is very sensitive to the structure and the morphology of the different scales of the electrode architecture involved in the electronic transport.
Foam structures with epoxy as the matrix and both carbon nanotubes (CNTs) and their hybrids with graphene oxide (GO-CNTs) as absorbers were fabricated, and their microwave absorbing and ...electromagnetic properties were investigated in the frequency range of 1–18 GHz. The fillers and bubbles were uniformly distributed in the composites. The complex permittivity and electrical conductivity of the composites increased as the fillers’ content increasing. The best performance of the reflection loss (RL) can be obtained for a foam structure with 0.5 wt% GO-CNTs, which had a RL peak value of −20dB with a −10 dB range of 5.3 GHz (10.8–16.1 GHz). Multi-layered structures were also discussed in this work, a RL peak value of −40dB with a −10dB range of 7.1 GHz (9.9–17 GHz) had been obtained by combining two foam structures, which are 2 mm thick 0.5 wt% GO-CNTs/epoxy and 1 mm thick 2.0 wt% GO-CNTs/epoxy. Furthermore, the −10dB range can reach 11.5 GHz (6.5–18 GHz) when combining 2.6 mm thick 0.5 wt% GO-CNTs/epoxy and 1.3 mm thick 2.0 wt% GO-CNTs/epoxy.
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To expand the application of insulating glass fiber (GF) in the field of microwave absorption, one type of GF hybrids with carbon nanotubes (CNTs) and nickel (Ni) was successfully synthesized by ...chemical vapor deposition and electroless plating methods. By changing the reaction conditions, the morphology of GF hybrids including CNT's length, CNT's growth density, and Ni′s thickness could be adjusted. The as‐produced hybrids were used as multifunctional reinforcement to fabricate epoxy composites. The dielectric properties of composites were particularly measured from 1 to 18 GHz. It was found that the variation of GF hybrids structure significantly changed the dielectric properties of the composites in the tested frequency range. Furthermore, the analytical simulation work based on the experimental results was conducted for optimizing the structural parameters of multilayered composites. The results showed that the best reflection loss of −60 dB with a −10 dB range of 5.6 GHz could be obtained in an absorber with a triple‐layered structure composed by GF‐CNTs/epoxy with different CNT contents and GF‐CNTs@Ni/epoxy. Thus, the proposed hybrid method might be quite efficient for developing composites that can achieve high‐performance electromagnetic absorbing.
The permittivity and conductivity of a porous composite consisting of a mixture of a lithium-ion battery electrode material, LiNi0.5Mn0.3Co0.2O2 (NMC532), and a polymeric binder, poly(vinylidene ...fluoride-co-hexafluoropropylene) (PVdF-HFP), were simultaneously measured by broadband dielectric spectroscopy (BDS). The composite was either dry or wetted with a conventional battery electrolyte LP30, LiPF6 in ethylene carbonate/dimethylcarbonate (EC/DMC) or a mixture of electrolytic solvents (EC/DMC). The experimental results show that the electronic conductivity of NMC532 was much higher than that obtained with LiNi0.33Mn0.33Co0.33O2 (NMC333). In addition, a strong influence of liquids was evidenced. Dipolar species (in particular, EC dipoles) and ions (in particular, PF6– in LP30) considerably increased the surface conductivity of NMC532 clusters, leading to a facilitated electronic transfer from one cluster to another. The effective ionic conductivity was measured and compared to the ionic conductivity of the electrolyte to express the tortuosity factor of this composite electrode.
This work aims at better understanding the interactions existing between the liquid electrolyte and the solid composite electrode in a Li-ion battery. We substituted the common active material (e.g. ...LiNi1/3Mn1/3Co1/3O2 or LiFePO4) by an insulating (inactive) γ-Al2O3 compound in order to detect and evidence the interaction between the carbon black electronic additive and the liquid electrolyte. Our study presents the characterization of charge (electrons and ions) transport at different scales by combining a high-frequency analysis performed by broadband dielectric spectroscopy (BDS, up to 1010 Hz), along with a low-frequency analysis performed by electrochemical impedance spectroscopy (EIS, down to 10−3 Hz). Two carbon black materials with two different specific surface areas (80 m2.g−1 and 65 m2.g−1, respectively) were studied. The electronic percolation threshold and the kinetics of impregnation of the hierarchical composite electrode by the liquid electrolyte have been determined with respect to the carbon black content. The significant influence of the adsorbtion of ions at the carbon black surface on the electrons transport is particularly highlighted and explained.
The permittivity and conductivity of a porous composite consisting of a mixture of a lithium-ion battery electrode material, LiNi0.5Mn0.3Co0.2O2 (NMC532), and a polymeric binder, poly(vinylidene ...fluoride-co-hexafluoropropylene) (PVdF-HFP), were simultaneously measured by broadband dielectric spectroscopy (BDS). The composite was either dry or wetted with a conventional battery electrolyte LP30, LiPF6 in ethylene carbonate/dimethylcarbonate (EC/DMC) or a mixture of electrolytic solvents (EC/DMC). The experimental results show that the electronic conductivity of NMC532 was much higher than that obtained with LiNi0.33Mn0.33Co0.33O2 (NMC333). In addition, a strong influence of liquids was evidenced. Dipolar species (in particular, EC dipoles) and ions (in particular, PF6 – in LP30) considerably increased the surface conductivity of NMC532 clusters, leading to a facilitated electronic transfer from one cluster to another. The effective ionic conductivity was measured and compared to the ionic conductivity of the electrolyte to express the tortuosity factor of this composite electrode.
The article investigates the shielding effectiveness (SE) of a metallic enclosure with a multilayer composite cover over a wide frequency range, from near-field magnetic shielding (1 Hz-1 MHz) to ...far-field electromagnetic shielding (4-14 GHz). Two enclosures are considered: a conductive enclosure made of aluminum and a magnetic enclosure made of steel. The multilayer composite is a trilayer combining a thin conductive layer of graphene and a thin magnetic layer of a Fe-Ni alloy on either side of a fiberglass plate. To determine the SE of these enclosures in both low-frequency and high-frequency approaches, two experimental setups and two numerical models are developed. The use of the composite cover, instead of the metallic one, gives a similar level of SE in the far-field and a higher specific SE (i.e., SE divided by the material density) in the near-field from 1 Hz to 2 kHz. Such quantitative analysis is the first step to designing practical enclosures entirely covered with composite panels to face electromagnetic compatibility (EMC) constraints in embedded systems.
•Broadband dielectric spectroscopy measures the multiscale electronic conductivity from macroscopic to interatomic sizes.•There is an influence of the surface states on the electronic transfer of ...powdered materials (e.g. thin insulating layer of Li2CO3 on LiNiO2 and carbon coating on LiFePO4).•Electrical relaxations resulting from the interfacial polarizations at the different scales of the carbon black network are evidenced.
Broadband dielectric spectroscopy (BDS) is used to measure complex permittivity and conductivity of conducting materials for lithium batteries at frequencies from a few Hz to several GHz with network and impedance analysers. Under the influence of an electric field, there will be charge density fluctuations in the conductor mainly due to electronic transfer. These fluctuations result in dielectric relaxations for frequencies below 100GHz. The materials are compacted powders in which each element (particles, agglomerates of particles) can have different sizes and morphologies. In the present review, studies are reported on the influence of surface states in LiNiO2 (ageing and degradation in air) and LiFePO4 (carbon coating thin layer), and on a composite electrode based on the lithium trivanadate (Li1.1V3O8) active material. The results have shown that the BDS technique is very sensitive to the different scales of materials architectures involved in electronic transport, from interatomic distances to macroscopic sizes.
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