For Zn-ion batteries, manganese dioxide (MnO2) is a highly promising cathode material due to its unique polymorphs (alpha, R, gamma, S), which contribute to distinct tunnel structures and enhanced ion conductivity. Despite its capabilities, MnO2 has still suffered from poor structural stability and low ionic and electronic conductivity. In this study, the densification of four distinct polymorphs of MnO2 was investigated to achieve structures relevant to ion transport by cold sintering. By systematically controlling the cold sintering temperature, the densification of each polymorph was successfully achieved without inducing undesirable phase transitions, enabling precise control over relative density. Electrochemical impedance spectroscopy confirms that cold-sintered MnO2 can function effectively as a cathode, with electrochemical performance closely related to sintering-induced microstructural evolution and density. These findings highlight the feasibility of cold sintering as a viable route for tailoring the densification and functional properties of MnO2-based cathodes, offering a promising approach for next-generation cathodes.

Bipolar plates account for almost 29% of the fuel cell stack costs and hence cost-effective manufacturing methods for making the bipolar plates are of paramount importance. Current manufacturing technologies for graphite bipolar plates require consolidation of graphite precursor materials using compression or injection molding followed by high temperature treatment for baking and graphitization. In contrast, in this investigation, we demonstrate direct consolidation of graphite powders without the use of any coal, petroleum or polymer binders resulting in significant reduction of time during compression molding as well as elimination of the need for additional heat treatment. Graphite particles were electrolessly coated with copper particles and subject to uniaxial compression at 100°C to produce a highly dense compact with relative density of ~ 98%, The process resulted in improving the flexural strength of the compact by almost ~50%. TEM investigation of the graphite particle interfaces revealed that copper undergoes creep deformation that aids in strengthening the compacts. The paper will describe the underlying mechanisms for the binderless production of graphite compacts which could be potentially useful for energy and cost-effective production of bipolar plates for fuel cells and flow batteries.

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Soft magnetic composites are powder metal products under development as an alternative to 2D laminates in electric motor applications. The 3D design of SMCs offers greater energy efficiency but poses a challenge to maintain adequate strength properties required for application. Soft magnetic composites are fabricated through compaction and heat treatment of iron particles coated with insulated coating to form a dense compact. The soft magnetic properties of the compact are affected by the properties of the iron powder, density of compact as well as the efficacy of forming uniform thin insulating coating at the particle boundary. Additionally, the strength of the compact is also affected by the nature of the insulating boundary at the particle interfaces. We report a low temperature process that involves cold sintering phenomenon to densify and strengthen soft magnetic composites. Iron powders have been modified using a co-precipitation method that forms a hydrated copper/iron oxalate coating on individual iron particles. Warm compaction of the modified iron powders at 100°C resulted in a highly dense soft magnetic composite which demonstrated ~ 3x improvement in strength. The compacts can be further heat treated in air at higher temperatures to form high strength oxide coating iron based soft magnetic composites. Results of the AC and DC magnetic measurements of fabricated cold sintered toroid compacts made as a function of heat treatment temperature reveal that DC permeability increased with heat treatment temperature. Analysis of AC core loss data showed that hysteresis power losses dominated the performance at lower heat treatment temperatures (< 300°C) beyond which dynamic core losses significantly increased.

Soft magnetic compositesSoft magnetic composite are a necessary component to produce efficient electric vehicles. However, the relationship between structure and material properties results in a nearly inevitable trade-off between efficiency and strength. The work presented here investigates a means of directly addressing improvement in both strength and magnetic properties by use of cold sinteringCold sintering technique. The technique utilizes surface modificationModification of individual particles which are warm compacted to improve strength and provide the necessary insulating properties to attain the characteristic soft magnetic properties required for use in electric motors. Materials are investigated using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy, 3-point bending tests, 4-point probe tests, permeability measurement, and AC and DC magnetic testing. These characterization methods are used to qualitatively and quantitatively inspect the applicability of the material as a soft magnetic compositeSoft magnetic composite. Finally, this study contributes to understanding how to improve strength at relatively low temperature via cold sinteringCold sintering method.

Crosslinked polyethylene (XLPE) is a key material for power cable insulation due to its superior electrical properties. It is co-extruded with a semiconducting “semicon” layer, which is significantly more conductive than XLPE due to the incorporation of carbon black. Understanding the electrical properties of the XLPE/semicon bilayer and the interface between them is critical due to their common use. Two techniques were used to study electrical properties of XLPE and XLPE/semicon bilayers. One was current-voltage measurements, which analyzed resistivity as a function of time. The other was high-voltage polarization, which analyzed polarizability and dielectric loss as a function of electrical field. Thin films of PE and semicon were made via melt pressing. Dicumyl peroxide was infused to the beads prior to melt pressing such that XLPE was formed. All samples were degassed to remove DCP byproducts. Semicon/polyethylene bilayers were made by pressing the two layers together. LDPE and LDPE/semicon were also studied. Bulk brass electrodes were used. Current-voltage measurements showed that adding the semicon layer increased conductivity by an order of magnitude. Polarization measurements revealed that significant enhancement in the dielectric loss occurred at electric fields of 15 kV/mm and above. Polyethylene by itself and semicon bilayer samples had distinct electrical properties, and thus a proper understanding of the performance of XLPE in power cables required analyzing both. Further work is suggested that focuses on correlating changes in measured conductivity to the nature of the material interface (e.g., via enhanced charge injection and/or introduction of charge carriers).

Given the availability of a wide range of properties not possessed by individual materials, nanocomposites based on conducting polymers and inorganic materials have attracted much deserved attention. However, there has been little attempt to optimize the synthesis and thermal properties of polyaniline–clay nanocomposites. In this study, the synthesis and thermal properties of polyaniline (PANi) and polyaniline–clay nanocomposites (PACN) were performed by systematically varying the feed composition. Both PANi and polyaniline–montmorillonite (MMT) nanocomposites were prepared by using ammonium persulfate (APS) as the oxidant. The chemical structure of the nanocomposites was studied by Fourier transform infrared spectroscopy (FTIR). FTIR spectra confirmed the presence of clay in the nanocomposites and the existence of mainly the emiraldine form of PANi. Thermal analysis was performed by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The morphology and structure of PANi and PACN were studied by scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM). Our results confirm the intercalation and partial exfoliation of clay. This study also showed that increasing the oxidant concentration resulted in decreasing thermal stability and melting temperature of PANi. The reinforcement of PANi with MMT resulted in increased thermal stability and increased melting point of PANi. It was also shown that the addition of only about 0.1 wt% of APS resulted in an optimal thermal stability and melting point for PANi.

The transient current in low-density polyethylene (LDPE) is studied, particularly in the presence of the small organic molecule acetophenone (ACP). Crosslinked LDPE is used extensively in high-voltage power transmission, and acetophenone is a common byproduct of the crosslinking chemistry. Time-dependent current measurements of LDPE with and without ACP soaked into the polymer as well as at one or both electrodes are performed by applying step voltages. The results demonstrate that the presence of ACP causes a deviation in the predicted power-law current decay, suggesting that electron and hole injection at the anode and cathode, respectively, are affected by the presence of this small organic molecule. ACP contributes both to the ionic conduction and charge hopping mechanism. The charge mobility depends on the applied electric field and the sample thickness. The results suggests that the dispersive charge transport phenomenon influences the measured current. This study shows how such a molecule may alter charge transport in polyethylene.

The surface of iron powder has been modified using phosphoric acid to facilitate a low temperature densification and strengthening process under warm compaction. Cold sintering of the compacts results in a co-continuous phosphate interphase between iron particles that provide both enhanced green strength and green density like the process that has been successfully introduced in low temperature densification of ceramic materials. Relative density as high as 95% along with transverse rupture strength of ~ 75 MPa, which is almost six times that of conventional powdered metal iron compact and 2.5 times that of warm compacted controls was achieved. Dilatometry study at different pressures showed a small but significant improvement in densification process during cold sintering relative to the larger densification of conventional warm compaction. Strength model based on microstructural analysis as well as in situ DRIFTS experiments revealed the nature of the interphase that imparted the large cohesive strength under the cold sintered assisted warm compaction. The process was conducive to produce iron compacts for green machining and various machining operations have been demonstrated. Furthermore, the samples when subjected to high temperature sintering yielded a fully sintered iron compact with density > 7.2 g cm-3 and transverse rupture strength as high as 780 MPa. All in all, there are major new opportunities with the cold sintered assisted warm compaction of powdered metals, that will also be discussed.

Iron powder metallurgy is a well-established field in the powder metal (PM) industry due to its ease of processing and appreciable mechanical properties. One area that can contribute significantly to increased production and warrants more study is green machining. Additionally, our current global environmental state calls for more energy efficient processing methods. Cold sintering process (CSP) of metals may provide a means for decreasing required sintering temperature for metal via liquid phase sintering. Our application of CSP utilizes surface modification of iron particles to form an ultrathin hydrated phosphate layer (~10 nm). The hydrated layer promotes driving force for rearrangement and densification under warm compaction to yield compacts with significantly increased green strength up to 70 MPa. This method is currently under investigation for the impact of alloyed iron as well. Implementation of CSP for iron may result in increased mechanical properties, decreased sintering temperature requirements, and decreased energy consumption.

Crosslinked polyethylene (XLPE) is a key material used for power cable insulation due to its electrical properties and structure. Here, it was shown that the technique of broadband dielectric spectroscopy can be used to analyze both by extracting the temperature coefficient of capacitance (TCC), dielectric loss, and AC conductivity. TCC for low-density polyethylene (LDPE) can be directly compared to its linear thermal expansion coefficient and used as a tool to compare different types of polyethylene. Degassing, a thermal treatment to remove volatile species and increase crystallinity, can be used to control TCC magnitude. In general, changes in the TCC magnitude are reflective of changes in the crystallinity and byproduct concentrations. Degassing also reduced the dielectric loss for both due to morphological changes and byproduct removal. However, it only reduces conductivity at elevated temperatures such as 90 °C for XLPE. Other processing parameters, as well as excessive byproduct concentrations, were also seen to influence TCC, dielectric loss, and conductivity.

All-solid-state Li-ion batteries (ASSB) are one of the most attractive next generation batteries for large scale application due to improved safety and higher energy density. However, the high temperature process required for densification of the solid-state electrolytes and for co-sintering of the multilayered ASSB is still a major challenge for large scale fabrication. In this study, a low temperature process, named cold sintering process, is applied to co-sinter all the layers in the ASSB at a low temperature. The cold sintered ASSB, a full-cell of Li 4 Ti 5 O 12 /Li 7 La 3 Zr 2 O 12 /LiFePO 4, has densified microstructures and exhibits impressive electrochemical performance. The ASSB delivers high capacity of 140 mAh g −1 at 0.1 C, rate capability of up to 2 C with 85 mAh g −1 , and 90% capacity retention over 100 cycles at room temperature under a current density of 0.2 C.

In this study, the byproduct-driven conduction current in LDPE was investigated. We built an experimental fixture to measure bulk conductivity in LDPE soaked with byproducts. Ohmic conduction was observed below 10 kV/mm. At above 10 kV/mm, space charge limited current (SCLC) predicts observed conduction in LDPE soaked with byproducts. It is found that the addition of byproducts introduces charge traps with discrete energy levels which dominate conduction. Degassed samples, on the other hand, show slopes of greater than 2.5 in a current-voltage log-log plot which was attributed to the charge traps with continuous energy levels. By analyzing the thickness dependence of the current, we observed a transition from electrode- to bulk-limited current at above 20 kV/mm for acetophenone- and α-cumyl alcohol-soaked samples. The α-methylstyrene-soaked samples only show electrode-limited current.

Polymer dielectrics with low-loss and high-temperature tolerance are extremely desirable as electrical energy storage materials for advanced electronics and electrical power applications. They can allow fast switching rates during power conversion and therefore achieve high power densities without thermal issues. Here, we explore polypropylene (PP), the state of the art dielectric polymer, and present an innovative approach to substantially improve the thermal stability and concurrently reduce the dielectric loss of PP. In particular, cross-linkable antioxidant groups, hindered phenol (HP), are incorporated into PP via well-controlled chemical synthesis. The grafted HP can simultaneously serve as radical scavenger and cross-linker, thereby constraining thermally decomposed radicals and charge transport in the synthesized PP-HP copolymer. As a result, the upper-temperature limit of PP-HP is greatly extended to 190 °C and the electrical loss is even gradually reduced upon thermal annealing. The copolymer after heating under 190 °C exhibits better dielectric properties than the PP without any thermal treatment. The experimental results indicate that the PP-HP copolymers are promising materials for high-temperature, low-loss, and high-voltage dielectric applications.

The present study demonstrates a synergistic effect with the addition of low loading levels of boron nitride filler in silicone rubber that resulted in significant improvement in both ac breakdown strength and thermal conductivity of silicone rubber composites. Our results show that addition of 2.5 vol% and 7 vol% of h-BN platelets improved thermal conductivity of silicone rubber composites by 25% and 65% respectively. The ac breakdown strength of silicone rubber composites was investigated by varying surface area and particle size of hexagonal boron nitride (h-BN) platelets. The breakdown strength of composites with only 2.5 vol% of low surface area boron nitride (0075) was enhanced by 20% and with high surface area boron nitride (7HS) was improved by 30%. The improvement in ac breakdown strength was primarily attributed to effective heat dissipation in the composite as well as low dielectric loss performance of the composite and was dependent upon the textural properties of boron nitride fillers.

The present research work was aimed at improving the high field dielectric properties of silicone rubber (SR) composites used for power cable insulation. Liquid silicone rubber composites were developed using two types of clays as filler materials; organically modified montmorillonite (ommt) and calcined, surface treated kaolin with the commercial name Translink 37 (T37). The results revealed that the surface chemistry of the clay had a distinct effect on both dispersion as well as electrical performance of silicone rubber-clay composites. We observed that surface treated kaolin (T37) were well dispersed in the SR matrix, but had adverse impact on the crosslinking kinetics of liquid silicone rubber resulting in higher dielectric loss at low frequencies. On the other hand, organically modified clay showed poor dispersion in the silicone rubber matrix while exhibiting much lower dc conductivity characteristics at high temperature. The agglomerated ommt macroparticles introduced the interfacial traps in SR matrix and charge carriers migration was limited within the matrix.