Critical Current Density Research Articles

Comparison of Current Induced Domain Wall Motion Driven by Spin Transfer Torque and by Spin Orbit Torque in Ferrimagnetic GdFeCo Wires

Current-induced domain wall motion (CIDWM) in magnetic wires can be driven by spin transfer torque (STT) originating from transferring angular momentums of spin-polarized conducting electrons to the magnetic DW and can be driven by spin orbit torque (SOT) originating from the spin Hall effect (SHE) in a heavy metal layer and Dzyaloshinsky Moriya (DMI) generated at an interface between a heavy metal layer and a magnetic layer. In this work, we carried out a comparative study of CIDWM driven by STT and by SOT in ferrimagnetic GdFeCo wires with magnetic perpendicular anisotropy based on structures of SiN (10 nm)/GdFeCo (8 nm)/SiN (10 nm) and Pt (5 nm)/GdFeCo (8 nm)/SiN (10 nm). We found that CIDWM driven by SOT exhibited a much lower critical current density (JC), and much higher DW mobility (µDW). Our work might be useful for the realization and the development of low-power and high-speed memory devices.

Improved interfacial stability of all-solid-state batteries using cation-anion co-doped glass electrolytes

The electrochemical performance of all-solid-state batteries needs to be improved by addressing the poor stability against the lithium metal anode and the high interfacial resistance at the cathode–solid electrolyte interface. Here, metal halide-doped Li7P2S8I–type (LPSI) solid electrolytes are synthesized that improve the electrochemical performance of all-solid-state batteries. The solid electrolytes exhibit a higher ionic conductivity value of 7.77 mS cm−1 than bare LPSI solid electrolytes of 3.96 mS cm−1, at room temperature. The metal halide-doped LPSI solid electrolyte is also stable against the lithium metal anode, with a calculated critical current density value of 1 mA cm−2. The fabricated all-solid-state battery shows high electrochemical performance with 99.2% specific capacity retention after 250 cycles at a 0.5 C rate. The results of post galvanostatic charge–discharge analysis confirms that the proposed metal halide-doped LPSI solid electrolyte exhibits improved interfacial stability compared to bare LPSI solid electrolytes.

Assessment of superconducting and structural stability of advanced Y-123 and Y-358 ceramics with Tb/Y substitution in main matrices

In this study, the performances of Y1-x(Tb)xBa2Cu3O7-δ (Y-123) and Y3-x(Tb)xBa5Cu8O18-δ (Y-358) advanced ceramics prepared by sol-gel preparation route are investigated by the advanced characterization methods including X-ray diffraction (XRD), temperature dependent resistivity (ρ-T), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and energy distribution spectroscopy (EDS) measurements and theoretical approaches. The EDS results illustrated that the Tb impurities were replaced successfully by the yttrium sites in the YBa2Cu3O7-y main matrix. Similarly, it was noted that the presence of excess impurities in the crystal structure led to the oxygenation problems. Electrical properties were determined by temperature dependent resistivity (ρ-T) measurements. ρ-T results indicated that Tb doping reduced the critical transition temperature (Tc) values for the transition to superconductivity for all samples in two YBCO phases. Although it appears to have negative effects of Tb ions on the number of mobile charge carrier concentrations in the σ antibonding in-plane Cu-O bonds, bipolaron formations in the polarizable lattices, oxidation states, and amplitude of the pair wave function of both phases, the other valuable properties (morphology, crystallinity quality, interaction between adjacent layers, critical current density, and flux pinning ability) were noted to improve remarkably in the case of the optimum amount in the Y-123 superconducting phase. In this context, the Y-358 superconducting phase was harshly affected by the substitution due to the change of the ortorombicity, localization problem, impurity phases, structure stabilization, crystal structure quality, crystallization system, homogeneities of oxidation states, oxygen ordering degree, and impurity scatterings. Besides, the analysis of the fluctuation induced conductivity indicated that the Y-123 ceramics with longer c-axis coherence length and less anisotropic nature exhibited well superconducting properties. Additionally, the doping ratio of x=0.01 led to the formation and distribution of more nucleation centers for the thermal fluxon motions of 2D pancake vortices. Similarly, the optimum Tb doped Y-123 system exhibited much durable to applied field strengths due to the best interaction quality between grains. Accordingly, this study recommended that the Y1-x(Tb)xBa2Cu3O7-δ advanced ceramic structure with new functionalities can find much more application areas in innovative, heavy-industrial technologies, and advanced engineering-related sectors.

Removal and Reoccurrence of LLZTO Surface Contaminants under Glovebox Conditions.

The reactivity of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolytes to form lithio-phobic species such as Li2CO3 on their surface when exposed to trace amounts of H2O and CO2 limits the progress of LLZTO-based solid-state batteries. Various treatments, such as annealing LLZTO within a glovebox or acid etching, aim at removing the surface contaminants, but a comprehensive understanding of the evolving LLZTO surface chemistry during and after these treatments is lacking. Here, glovebox-like H2O and CO2 conditions were recreated in a near ambient pressure X-ray photoelectron spectroscopy chamber to analyze the LLZTO surface under realistic conditions. We find that annealing LLZTO at 600 °C in this atmosphere effectively removes the surface contaminants, but a significant level of contamination reappears upon cooling down. In contrast, HCl(aq) acid etching demonstrates superior Li2CO3 removal and stable surface chemistry post treatment. To avoid air exposure during the acid treatment, an anhydrous HCl solution in diethyl ether was used directly within the glovebox. This novel acid etching strategy delivers the lowest lithium/LLZTO interfacial resistance and the highest critical current density.

Efficient magnetization switching induced by spin–orbit torque in perpendicularly magnetized Mn1+xCo2−xAl Heusler alloys

Perpendicularly magnetized Co-based Heusler alloys are promising candidates in high-performance spintronic devices. However, there is a contradiction between thermal stability and damping-like spin–orbit torque (SOT) efficiency in Co-based Heusler alloys with interface-induced perpendicular magnetic anisotropy (PMA). Here, we present epitaxially grown perpendicularly magnetized Mn1+xCo2−xAl (MCA) Heusler alloys through tetragonal distortion. Ferrimagnetism and distortion-induced PMA are obtained in MCA Heusler alloys. A large effective spin Hall angle (θeff) up to 0.33 is experimentally demonstrated in Pt/MCA bilayers, markedly surpassing that in conventional Pt/FM bilayers. Consequently, SOT-induced efficient magnetization switching is realized in Pt/MCA bilayers, with a critical switching current density (Jc) as low as 4 × 107 A/cm2. The large θeff and high SOT efficiency would be attributed to the staggered magnetic exchange torques in the ferrimagnetic MCA Heusler alloys. These findings demonstrate that perpendicularly magnetized ferrimagnetic MCA Heusler alloys are highly promising for high-density SOT-magnetic random-access memory with superior thermal stability and low power consumption.

Fabrication of high-entropy alloy superconducting wires by powder-in-tube method

High-entropy alloys (HEAs) are novel functional materials that exhibit excellent mechanical and chemical properties. Recent discovery of self-healing superconductivity of HEAs under ion irradiation suggests their great potential applications under extreme conditions such as in nuclear fusion reactors or space environments. Here, we report a fabrication of the HEA superconducting (SC) wires using the ex-situ powder-in-tube (PIT) technique for the first time, a crucial stepping stone to achieve various industrial and technological applications. The Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 HEA SC powder prepared by planetary ball milling was filled into Fe tubes, drawn into wires, and then sintered in evacuated quartz tubes at various temperatures. The HEA SC wire sintered at 700 °C for 1 h exhibits the highest critical current density (Jc) among the HEA SC wires sintered in the temperature range of 600 – 1000 °C. At 4.2 K, the Jc of this wire exceeds the common benchmark value of Jc = 100 kA cm−2, indicating the suitability of the HEA wire for large-scale applications, such as in high-field SC magnets. The SC transition temperature (Tc) of the HEA wire significantly increases from 5.10 K for the as-cast wire to 7.58 K with the sintering time (ts) of 30 min at 700 °C. The scaling of the flux pinning force as a function of the magnetic field indicates that normal point pinning plays a major role in achieving a high in-field Jc in HEA SC wires. These results underscore the significant potential of HEA superconductors for practical applications in high-field SC magnets, SC electric machines, and next-generation nuclear fusion reactors.

Fabrication of a 25.2 T NMR magnet for an extreme condition user facility in China

Abstract An ultra-high field magnet (> 20 T) is desirable to study material characteristics under extreme magnetic condition with the use of magnetic resonance for a higher signal-to-noise ratio, better sensitivity and a higher spectral resolution. The fabrication of an ultra-high field magnet requires high-temperature superconducting materials like REBSO and BSCCO, which have higher critical temperature and current density as compared to conventional low-temperature superconducting materials. Despite the benefits of BSCCO for better field homogeneity and stability due to its smaller screening currents, it is technically challenging to use it in magnet fabrication due to the greater variations in tape thickness and width. In this highlighted study, an optimization procedure was developed to randomly re-order the wound double-pancake coils as well as optimize the winding turns based on pre-winding measurements. Such optimizations enable the fabrication of a magnet with high homogeneity that is suitable for use in nuclear magnetic resonance.

Enhanced Spin-orbit torques in Graphene by Pt adatoms decoration

Abstract Graphene (Gr) with widely acclaimed characteristics, such as exceptionally long spin diffusion length at room temperature, provides an outstanding platform for spintronics. However, its inherent weak spin-orbit coupling (SOC) has limited its efficiency for generating the spin currents in order to control the magnetization switching process for the application in spintronics memories. Following the theoretical prediction on the enhancement of SOC in Gr by heavy atoms adsorption, here we experimentally observe a sizeable spin-orbit torques (SOTs) in Gr by the decoration of its surface with Pt adatoms in Gr/Pt(t Pt )/FeNi trilayers with the optimal damping-like SOT efficiency around 0.55 by 0.6-nm-thick Pt layer adsorption. The value is nearly four times larger than that of the Pt/FeNi sample without Gr and nearly twice as large as that of the Gr/FeNi sample without Pt adsorption. The efficiency of the enhanced SOT in Gr by Pt adatoms is also demonstrated by the field-free SOT magnetization switching process with a relatively low critical current density around 5.4 MA/cm2 in Gr/Pt/FeNi trilayers with the in-plane magnetic anisotropy. These findings pave the way for Gr spintronics application, offering solutions for future low power consumption memories.

Improvement of plastic deformation property and current carrying capacity of Bi2212 wires through low oxygen partial pressure post-annealing of precursor

The performance of superconducting magnets is greatly dependent on the size and uniformity of the superconducting filaments within the wire. However, in the fabrication of Bi2Sr2CaCu2Ox (Bi2212) wires using ceramic oxide as the superconducting filaments, we face multiple challenges including filament fragility, poor uniformity, and non-smooth Ag/superconductor interfaces. These challenges primarily stem from the significantly lower plastic deformation capability of ceramic oxide powder filaments compared to metal matrices. To address these challenges, this study focuses on the modification of ceramic oxide precursor powders. Through the utilization of low-temperature, low oxygen partial pressure (pO2) heat treatment, we have observed significant changes in the Cu chemical states and lattice parameters within the Bi2212 grains. These alterations have proven to be highly effective in reducing the energy required for grain sliding and, in turn, enhancing the plastic deformation properties of the Bi2212 oxide filament. Furthermore, post-annealing the oxide powder under low pO2 conditions narrows the gap in plastic deformability between the Ag sheath and the oxide filaments, resulting in improved filament uniformity and a smoother Ag/oxide interface in Bi2212 wires. Notably, the Bi2212 grains exhibit an orderly arrangement within the wires. As a result of these improvements, the critical current density (Jc) of the final wires increases by an impressive 70 %. The outcomes of this study are not only crucial for producing Bi2212 magnets with higher magnetic field strength, improved magnetic field uniformity, and enhanced operational stability, but also offer fresh insights and methodologies for advancing the field of superconducting materials.

Recent development in high temperature superconductor: Principle, materials, and applications

Superconducting materials, discovered in the early twentieth century, have fascinated scientists with their unique attributes. This review provides a thorough exploration of superconductivity, tailored for newcomers, aiming to be a foundational resource for future research. It traces the evolution of different superconductors, including traditional, cuprate, and non-copper oxide types, detailing their specific characteristics. Central to the review is the examination of theoretical foundations, particularly the BCS theory, and the diverse applications of superconductors in high-performance magnets, energy transmission, and quantum computing. However, the practical deployment of superconductors is limited by challenges, notably their operation at extremely low temperatures, hindering widespread use. Furthermore, economic and technical difficulties in production and maintenance persist. To advance superconductors' potential, research must focus on enhancing critical temperatures and current density and developing cost-effective manufacturing techniques. This will enable novel applications in energy, transportation, and healthcare, driving technological progress.

A newly developed 10 kA-level HTS conductor: innovative tenon-mortise-based modularized conductor (TMMC) based on China ancient architecture

We proposed a new type of high-temperature superconducting (HTS) conductor concept: modularized conductors (MCs) connected by Chinese traditional tenon-mortise (TM) connection structure, referred as TMMC (tenon-mortise modularized conductor). The conductor consisted of multiple concentric round sub-conductors with slots for stacking rare-earth-barium-copper-oxide (REBCO) tapes. Innovatively, the REBCO stacks in the adjacent sub-conductors were arranged with the fully-misaligned configuration to enhance the critical current’s isotropy with respect to magnetic field and reduce ac loss. For example, the angle between the adjacent stacks in the two adjacent sub-conductors was 45° if each sub-conductor contains 4 REBCO stacks. In order to construct the fully-misaligned configuration, the sub-conductors were designed with two open half-circular formers and connected by TM structure which makes the conductor modularized and simply to assembly and disassembly. Based on the design concept, a prototype conductor containing 160 REBCO tapes distributed in the four concentric sub-conductors was fabricated. The conductor’s measured critical current was 13.69 kA at 77 K and self-field, which was consistent to the simulation result. In order to further improve the TMMC’s engineering critical current density (J ce) and bending performance, we proposed two enhancement approaches: reducing the former’s thickness and re-arrange stacks in the outer sub-conductors. With the enhancements, both TMMC’s radius and J ce were comparable to the existing slotted-core conductor. The study shows the TMMC’s advantages of non-twisted structures, easy assembly, high-current carrying and low ac losses, which made it promising for constructing large-scale scientific devices.

Superior Superconducting Properties Realized in Quaternary La-Y-Ce Hydrides at Moderate Pressures.

The recent revolution in the superconductivity field stems from hydride superconductors. Multicomponent hydrides provide a crucial platform for tracking high-temperature superconductors. Besides high superconducting transition temperature (Tc), achieving both giant upper critical magnetic field [μ0Hc2(0)] and high critical current density [Jc(0)] is also key to the latent potential of the application for hydride superconductors. In this work, we have successfully synthesized quaternary La-Y-Ce hydrides with excellent properties under moderate pressure by using the concept of "entropy engineering." The obtained temperature dependence of the resistance provides evidence for the superconductivity of Fm3m-(La,Y,Ce)H10, with the maximum Tc ∼ 190 K (at 112 GPa). Notably, Fm3m-(La,Y,Ce)H10 boasts exceptional properties: μ0Hc2(0) reaching 292 T and Jc(0) surpassing 4.61 × 107 A/cm2. Compared with the binary LaH10/YH10, we find that the Fm3m structure in (La,Y,Ce)H10 can be stable at relatively low pressures (112 GPa). These results indicate that multicomponent hydrides can significantly enhance the superconducting properties and regulate stabilizing pressure through the application of "entropy engineering." This work stimulates the experimental exploration of multihydride superconductors and also provides a reference for the search of room-temperature superconductors in more diversified hydride materials in the future.

An open-source 3D FE quench simulation tool for no-insulation HTS pancake coils

A new module, Pancake3D, of the open-source finite element quench simulator (FiQuS) has been developed in order to perform transient simulations of no-insulation (NI) high-temperature superconducting pancake coils in three-dimensions. FiQuS/Pancake3D can perform magnetodynamic or coupled magneto-thermal simulations. Thanks to the use of thin shell approximations, an H→−ϕ formulation, and anisotropic homogenization techniques, each turn can be resolved on the mesh level in an efficient and robust manner. FiQuS/Pancake3D relies on pre-formulated finite-element (FE) formulations and numerical approaches that are programmatically adjusted based on a text input file. In this paper, the functionalities and capabilities of FiQuS/Pancake3D are presented. The challenges of FE simulation of NI coils and how FiQuS/Pancake3D addresses them are explained. To highlight the functionalities, the results of a magneto-thermal analysis of a double pancake coil with 40 turns per pancake with local degradation of the critical current density are conducted and discussed. Furthermore, a parameter sweep of the size of this local degradation is presented. All FiQuS input files for reproducing the simulations are provided.

Zwitterionic Cellulose-based Polymer Electrolyte Enabled by Aqueous Solution Casting for High-performance Solid-state Batteries.

Polyethylene oxide (PEO)-based solid-state batteries hold great promise as the next-generation batteries with high energy density and high safety. However, PEO-based electrolytes encounter certain limitations, including inferior ionic conductivity, low Li+ transference number, and poor mechanical strength. Herein, we aim to simultaneously address these issues by utilizing one-dimensional zwitterionic cellulose nanofiber (ZCNF) as fillers for PEO-based electrolytes using a simple aqueous solution casting method. Multiple characterizations and theoretical calculations demonstrate that the unique zwitterionic structure imparts ZCNF with various functions, such as disrupting PEO crystallization, dissociating lithium salts, anchoring anions through cationic groups, accelerating Li+ migration by anionic groups, as well as its inherent reinforcement effect. As a result, the prepared PL-ZCNF electrolyte exhibits remarkable ionic conductivity (5.37 × 10-4 S cm-1) and Li+ transference number (0.62) at 60 °C without sacrificing mechanical strength (9.2 MPa), together with high critical current density of 1.1 mA cm-2. Attributed to these merits of PL-ZCNF, the LiFePO4|PL-ZCNF|Li solid-state full-cell delivers exceptional rate capability and cycling performance (900 cycles at 5 C). Notably, the assembled pouch-cell can maintain steady operation over 1000 cycles with an impressive 93.7% capacity retention at 0.5 C and 60 °C, highlighting the great potential of PL-ZCNF for practical applications.

Zwitterionic Cellulose‐based Polymer Electrolyte Enabled by Aqueous Solution Casting for High‐performance Solid‐state Batteries

Polyethylene oxide (PEO)‐based solid‐state batteries hold great promise as the next‐generation batteries with high energy density and high safety. However, PEO‐based electrolytes encounter certain limitations, including inferior ionic conductivity, low Li+ transference number, and poor mechanical strength. Herein, we aim to simultaneously address these issues by utilizing one‐dimensional zwitterionic cellulose nanofiber (ZCNF) as fillers for PEO‐based electrolytes using a simple aqueous solution casting method. Multiple characterizations and theoretical calculations demonstrate that the unique zwitterionic structure imparts ZCNF with various functions, such as disrupting PEO crystallization, dissociating lithium salts, anchoring anions through cationic groups, accelerating Li+ migration by anionic groups, as well as its inherent reinforcement effect. As a result, the prepared PL‐ZCNF electrolyte exhibits remarkable ionic conductivity (5.37 × 10−4 S cm−1) and Li+ transference number (0.62) at 60 °C without sacrificing mechanical strength (9.2 MPa), together with high critical current density of 1.1 mA cm−2. Attributed to these merits of PL‐ZCNF, the LiFePO4|PL‐ZCNF|Li solid‐state full‐cell delivers exceptional rate capability and cycling performance (900 cycles at 5 C). Notably, the assembled pouch‐cell can maintain steady operation over 1000 cycles with an impressive 93.7% capacity retention at 0.5 C and 60 °C, highlighting the great potential of PL‐ZCNF for practical applications.

Interfacial Design Strategy for Polymeric Lithium Metal Batteries with Superfast Charge‐Transfer Kinetics

AbstractInterfacial instability including the high charge‐transfer resistance and the uncontrolled lithium dendrite growth have severely restricted the safety, fast‐charging, and high‐power capabilities of solid‐state polymeric lithium metal batteries (PLMBs). Here, the study demonstrates the ionic nanoclusters self‐assembled between the lithium ions and a rigid‐rod sulfonated aromatic polyamide Poly 2,2′‐disulfonyl‐4,4′‐benzidine terephthalamide (PBDT) can facilitate uniform lithium deposition; meanwhile, realizing 102–103 times lower interfacial charge‐transfer resistance than PEO‐based electrolytes and excellent lithium dendrite suppression at the interfaces. The cells assembled with this solid‐state polymer electrolyte at room temperature show a record high critical current density (6 mA cm−2/3 mAh cm−2), 80% capacity retention at 10 000 cycles (5 C) with the LiFePO4 cathode. With the temperature increased to 80 °C, the cells enable almost 100% of the theoretical capacity at 3 C and high specific power density (20 kW kg−1). According to the Cryo‐TEM imaging and computational simulation results, it is concluded that these nanoscale self‐assembled ionic nanoclusters play a critical role in realizing the superfast charge‐transfer kinetics by balancing the pre‐exponential factor and activation energy at the lithium‐polymer space‐charge interfaces. This interfacial design strategy based on thermodynamically favored ion‐association and self‐assembly between the metal ions and the polyanions guarantees superior charge‐transfer kinetics in PLMBs.

Fracture mechanisms and suppressed temperature effects of YBCO superconducting materials dominated by grain boundaries

YBa2Cu3O7-δ (YBCO) superconducting materials are typical polycrystalline materials, and the presence of intrinsic grain boundaries (GBs) is the main reason that affects superconductivity, in which high-angle GBs lead to low critical current density. There is no doubt that GBs also play an important role in the mechanical properties and fracture mechanisms of YBCO superconducting materials. In this work, the uniaxial tensile molecular simulations have been performed to investigate the fracture mechanisms of YBCO superconducting materials dominated by different types of GBs. The (100) single crystal and (110) twinning boundary models have been employed as comparative references. The results show that the low-angle GBs of YBCO consist of discontinuous dislocation cores, while the high-angle GBs are composed of a series of structural unit arrangements. Meanwhile, Young's modulus and ultimate tensile strength of YBCO can be enhanced by twin boundaries, while the other GBs have different effects on Young's modulus and ultimate tensile strength. In addition, the expansion of dislocation cores and the deformation of characteristic structural units are the main fracture mechanisms. More significantly, a novel temperature effect has been found to be significantly suppressed under the high-angle GBs. These findings not only provide a deep understanding of the GB structures, but may also provide guidance for modulating the mechanical properties of YBCO superconducting materials.

A Flexible and Mechanical Robust All-Solid-State Polymer Electrolyte with Microphase Separated Structure for Lithium-Ion Battery.

Polyethylene oxide (PEO)-based electrolytes are the most widely used solid polymer electrolyte (SPE) due to their high safety, excellent ability to dissociate lithium salts, low cost, and ease of preparation. However, low ionic conductivity and narrow electrochemical stability window limit their potential for further development. "Polymer-in-salt" electrolytes exhibit superior electrochemical performance; however, the high lithium salt concentration makes the SPE mechanically fragile when facing lithium dendrites. Therefore, preparing an SPE that can withstand a high concentration of lithium salt while still maintaining good mechanical properties has become a valuable challenge. In this study, a macroscopically homogeneous but nanoscopically phase-separated polymer matrix was designed as an electrolyte that can withstand a high concentration of lithium salt while retaining good mechanical properties, and this study investigated changes in the Li+ solvation structure within the electrolyte and analyzed the reasons for the simultaneous achievement of good ionic conductivity (1.02 × 10-3 S cm-1 at 60 °C) and mechanical properties (7 MPa at room temperature). The formation of large ion clusters at the phase interface and selective enrichment of lithium salt in specific regions are found to play crucial roles, and the critical current density (CCD) can reach a value of 2.2 mA cm-2. This work demonstrates a promising design approach for polymer electrolytes that achieves an optimal balance between SPE conductivity and mechanical properties through microstructure control.

Structure design of 500 kVA HTS transformer and Joule loss in superconducting windings

HTS transformers can provide lower loss and higher efficiency with smaller size and lighter weight compared with traditional transformers. In this paper, we designed a 500 kVA HTS transformer and developed its simulation using finite element software based on the H-formulation, and the simulation incorporates a heat model and E-J power law. The simulation shows that there is a large radial flux leakage at the end of the low-voltage (LV) windings (superconducting windings), leading to a reduction in critical current density and an associated increase in joule loss in the LV winding. In order to reduce joule loss, various LV winding structures were designed. The results demonstrate that either increasing the axial distance between the coils at the LV winding end or installing a flux diverter outside the LV windings can effectively diminish the radial flux leakage at the LV winding end, consequently reducing joule loss in the LV winding. The impact of the size, position and relative permeability of the flux diverter on radial flux leakage and joule loss are also studied. These structure optimizations and the corresponding effects have important significance to the design of HTS transformers.

The impact of lithium carbonate on tape cast LLZO battery separators: a balanced interplay between lithium loss and relithiation

Ceramic membranes made of garnet Li7Zr3La2O12 (LLZO) are promising separators for lithium metal batteries because they are chemically stable to lithium metal and can resist the growth of lithium dendrites. Free-standing garnet separators can be produced on a large scale using tape casting and sintering slurries containing LLZO powder, but the quality of the separators is severely compromized by the protonation of the moisture-sensitive LLZO during processing and the irreversible loss of lithium during sintering. In this work, an approach is presented to mitigate the degradation of the LLZO and produce high quality separators using Li2CO3 as a source of excess lithium. By systematically investigating the effects of Li2CO3 addition during the different steps of the tape casting process and the intricate relationship between the protonation and relithiation of LLZO phase, the formation of highly protonated LLZO during ball milling was identified as the most critical step. It was shown that the addition of minimal amounts of Li2CO3 during wet milling effectively suppresses LLZO protonation and ensure the effectiveness of relithiation during subsequent sintering. Using this modified method, flat LLZO separators with a relative density of 95.3% were prepared in a simplified process with a significantly reduced excess lithium of only 5 mol% with respect to the stoichiometric LLZO, exhibiting an ionic conductivity of 0.18 mS cm−1 at room temperature and a critical current density of 1 mA cm−2 at 60°C for lithium stripping/plating.