Electronic Conductivity Research Articles

Transforming an Ionic Conductor into an Electronic Conductor via Crystallization: In Situ Evolution of Transference Numbers and Structure in (La,Sr)(Ga,Fe)O3‐x Perovskite Thin Films

AbstractMixed‐conducting perovskites are workhorse electrochemically active materials, but typical high‐temperature processing compromises their catalytic activity and chemo‐mechanical integrity. Low‐temperature pulsed laser deposition of amorphous films plus mild thermal annealing is an emerging route to form homogeneous mixed conductors with exceptional catalytic activity, but little is known about the evolution of the oxide‐ion transport and transference numbers during crystallization. Here the coupled evolution of ionic and electronic transport behavior and structure in room‐temperature‐grown amorphous (La,Sr)(Ga,Fe)O3‐x films as they crystallize is explored. In situ ac‐impedance spectroscopy with and without blocking electrodes, simultaneous capturingsynchrotron‐grazing‐incidence X‐ray diffraction, dc polarization, transmission electron microscopy, and molecular dynamics simulations are combined to evaluate isothermal and non‐isothermal crystallization effects and the role of grain boundaries on transference numbers. Ionic conductivity increases by ≈2 orders of magnitude during crystallization, with even larger increases in electronic conductivity. Consequently, as crystallinity increases, LSGF transitions from a predominantly ionic conductor to a predominantly electronic conductor. The roles of evolving lattice structural order, microstructure, and defect chemistry are examined. Grain boundaries appear relatively nonblocking electronically but significantly blocking ionically. The results demonstrate that ionic transference numbers can be tailored over a wide range by tuning crystallinity and microstructure without having to change the cation composition.

Design of Linear-Polymer-Coated Graphene Nanosheets with π-Conjugated Structure and Multi-Active-Center for Long-Lifespan and High-Rate Li-Storage Performance.

Organic material holds immense potential for Li-ion batteries (LIBs) due to their eco-friendly nature, high structural designability, abundant sources, and high theoretical capacity. However, the limited redox-active sites, low electronic conductivity, sluggish ionic diffusion, and high solubility hinder their practical application. Here, we reported the use of a linear polymer called poly(naphthalenetetracarboxylic dianhydride-pyrene-4,5,9,10-tetraone)-coated graphene nanosheets (NPT/rGO) as a cathode material for LIBs. The NPT polymer has a rotation angle of approximately 63° between each plane, which helps in exposing the active sites and preventing structural pulverization during cycling. The highly conjugated skeleton of the polymer, along with graphene, forms a synergistic effect through a π-π interaction. This combination enhances the conductivity and restricts solubility. Additionally, the linear structure of NPT and the two-dimensional rGO substrates work together to enhance charge transfer and ion diffusion rates, resulting in faster reaction kinetics. Consequently, NPT/rGO exhibits excellent electrochemical performance in terms of high capacity, superior cyclic stability, and good rate capability for LIBs. Moreover, through the combination of experimental investigations and theoretical simulations, a multiple electron reaction mechanism, an efficient Li-ion storage behavior, and a reversible dynamic evolution have been revealed. This study introduces a rational molecular design approach to enhance the electrochemical performance of polyimide derivatives, thereby contributing to the advancement of cutting-edge organic electrode materials for LIBs.

Pseudocapacitive TiNb0.8O4 microspheres for fast-charging and durable sodium storage

Titanium niobium oxides are promising anode materials for sodium-ion batteries (SIBs) due to their efficient ion diffusion channels. However, their poor electronic conductivity impedes the longevity of SIBs. To address these issues, core@shell TiNb0.8O4/C@C microspheres (TNO/C@C) have been developed to enhance electron conduction. The TNO/C@C, featuring a bulk and surface dual conductive configuration, outperforms pure TNO and other control samples such as TNO/C and TNO@C that rely solely on either bulk or surface electronic conductors. Thus, the TNO/C@C achieves a fast-charging rate of 200 C, allowing full charging in 2 s, and demonstrates long-term stability over 10,000 cycles. In-situ Raman analysis reveals a zero-strain feature during sodiation/desodiation, which minimizes structural degradation over repeated cycles. In-situ electrochemical impedance spectroscopy test indicates low electron resistance, enhancing both the rate capability and stability. Therefore, the bulk and surface dual conducting strategy offers new insights into robust and fast-charging SIBs.

Twist Proximity-Endowed Large Figure of Merit in a Band-Modulated CrI3/1T-MoS2 Moiré Superlattice.

Moiré superlattices with a robust twist proximity effect in the low-dimensional regime can facilitate nanoscale thermoelectric devices. In pristine systems, the low efficiency and lack of proficient control of thermoelectric properties impede desirable advancements in the field of energy conversion. In the present study, we demonstrate remarkable macroscopic thermoelectric response as a consequence of microscopic band structure modulation via the twist proximity in an engineered CrI3/1T-MoS2 moiré superlattice. The local twist effect, which leads to the microscopic phenomena of electron localization, results in a comprehensive electronic structure modulation. Consequently, these local effects convolute the macroscopic thermoelectric effect. Additionally, flat bands and angle-dependent metallic to semiconducting transitions are observed at 10.89, 23.41, and 30° twist angles. We correlate the observed phenomenon with the augmented spin-charge transport and interconversion via the twist proximity effect in its semiconducting phase. The estimated ultralow electronic and lattice thermal conductivities further corroborate with the observed large figure of merit and Seebeck coefficient. The maximum values of the Seebeck coefficient and figure of merit are estimated to be ∼413 μV/K and ∼4.3 at 200 K for 30° under the constant time relaxation approach. The twist-endowed outstanding thermoelectric effect in moiré superlattices with band modulation unveils a distinctive approach to establish efficient thermoelectric devices.

From Lab to Application: Challenges and Opportunities in Achieving Fast Charging with Polyanionic Cathodes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs), recognized for balanced energy density and cost-effectiveness, are positioned as a promising complement to lithium-ion batteries (LIBs) and a substitute for lead-acid batteries, particularly in low-speed electric vehicles and large-scale energy storage. Despite their extensive potential, concerns about range anxiety due to lower energy density underscore the importance of fast-charging technologies, which drives the exploration of high-rate electrode materials. Polyanionic cathode materials are emerging as promising candidates in this regard. However, their intrinsic limitation in electronic conductivity poses challenges for synchronized electron and ion transport, hindering their suitability for fast-charging applications. This review provides a comprehensive analysis of sodium ion migration during charging/discharging, highlighting it as a critical rate-limiting step for fast charging. By delving into intrinsic dynamics, key factors that constrain fast-charging characteristics are identified and summarized. Innovative modification routes are then introduced, with a focus on shortening migration paths and increasing diffusion coefficients, providing detailed insights into feasible strategies. Moreover, the discussion extends beyond half cells to full cells, addressing challenges and opportunities in transitioning polyanionic materials from the laboratory to practical applications. This review aims to offer valuable insights into the development of high-rate polyanionic cathodes, acknowledging their pivotal role in advancing fast-charging SIBs.

Dendrite-Free All-Solid-State Lithium Metal Batteries by In Situ Phase Transformation of the Soft Carbon-Li3N Interface Layer.

The accelerated formation of lithium dendrites has considerably impeded the advancement and practical deployment of all-solid-state lithium metal batteries (ASSLMBs). In this study, a soft carbon (SC)-Li3N interface layer was developed with both ionic and electronic conductivity, for which the in situ lithiation reaction not only lithiated SC into LiC6 with good electronic/ionic conductivity but also successfully transformed the mixed-phase Li3N into pure-phase β-Li3N with a high ionic conductivity/ion diffusion coefficient and stability to lithium metal. The mixed conductive interface layer facilitates fast Li+ transport at the interface and induces the homogeneous deposition of lithium metal inside it. This effectively inhibits the formation of lithium dendrites and greatly improves the performance of the ASSLMB. The ASSLMB assembled with the SC-Li3N interface layer exhibits high areal capacity (15 mA h cm-2), high current density (7.5 mA cm-2), and long cycle life (6000 cycles). These results indicate that this interface layer has great potential for practical applications in high-energy-density ASSLMBs.

Scaly MoS2/rGO Composite as an Anode Material for High-Performance Potassium-Ion Battery.

Potassium-ion batteries (PIBs) have been widely studied owing to the abundant reserves, widespread distribution, and easy extraction of potassium (K) resources. Molybdenum disulfide (MoS2) has received a great deal of attention as a key anode material for PIBs owing to its two-dimensional diffusion channels for K+ ions. However, due to its poor electronic conductivity and the huge influence of embedded K+ ions (with a large ionic radius of 3.6 Å) on MoS2 layer, MoS2 anodes exhibit a poor rate performance and easily collapsed structure. To address these issues, the common strategies are enlarging the interlayer spacing to reduce the mechanical strain and increasing the electronic conductivity by adding conductive agents. However, simultaneous implementation of the above strategies by simple methods is currently still a challenge. Herein, MoS2 anodes on reduced graphene oxide (MoS2/rGO) composite were prepared using one-step hydrothermal methods. Owing to the presence of rGO in the synthesis process, MoS2 possesses a unique scaled structure with large layer spacing, and the intrinsic conductivity of MoS2 is proved. As a result, MoS2/rGO composite anodes exhibit a larger rate performance and better cycle stability than that of anodes based on pure MoS2, and the direct mixtures of MoS2 and graphene oxide (MoS2-GO). This work suggests that the composite material of MoS2/rGO has infinite possibilities as a high-quality anode material for PIBs.

High-Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High-Performance Wearable Supercapacitors.

Construction advanced fibers with high Faradic activity and conductivity are effective to realize high energy density with sufficient redox reactions for fiber-based electrochemical supercapacitors (FESCs), yet it is generally at the sacrifice of kinetics and structural stability. Here, a high-entropy doping strategy is proposed to develop high-energy-density FESCs based on high-entropy doped metal oxide@graphene fiber composite (HE-MO@GF). Due to the synergistic participation of multi-metal elements via high-entropy doping, the HE-MO@GF features abundant oxygen vacancies from introducing various low-valence metal ions, lattice distortions, and optimized electronic structure. Consequently, the HE-MO@GF maintains sufficient active sites, a low diffusion barrier, fast adsorption kinetics, improved electronic conductivity, enhanced structural stability, and Faradaic reversibility. Thereinto, HE-MO@GF presents ultra-large areal capacitance (3673.74mFcm-2) and excellent rate performance (1446.78mFcm-2 at 30mAcm-2) in 6M KOH electrolyte. The HE-MO@GF-based solid-state FESCs also deliver high energy density (132.85µWhcm-2), good cycle performance (81.05% of capacity retention after 10,000 cycles), and robust tolerance to sweat erosion and multiple washing, which is woven into the textile to power various wearable devices (e.g., watch, badge and luminous glasses). This high-entropy strategy provides significant guidance for designing innovative fiber materials and highlights the development of next-generation wearable energy devices.

Heat Pulses in Electron Quantum Optics.

Electron quantum optics aims to realize ideas from the quantum theory of light with the role of photons being played by charge pulses in electronic conductors. Experimentally, the charge pulses are excited by time-dependent voltages; however, one could also generate heat pulses by heating and cooling an electrode. Here, we explore this intriguing idea by formulating a Floquet scattering theory of heat pulses in mesoscopic conductors. The adiabatic emission of heat pulses leads to a heat current that in linear response is given by the thermal conductance quantum. However, we also find a high-frequency component, which ensures that the fluctuation-dissipation theorem for heat currents, whose validity has been debated, is fulfilled. The heat pulses are uncharged, and we probe their electron-hole content by evaluating the partition noise in the outputs of a quantum point contact. We also employ a Hong-Ou-Mandel setup to examine if the pulses bunch or antibunch. Finally, to generate an electric current, we use a Mach-Zehnder interferometer that breaks the electron-hole symmetry and thereby enables a thermoelectric effect. Our Letter paves the way for systematic investigations of heat pulses in mesoscopic conductors, and it may stimulate future experiments.

Zero-strain Co-doped Na2FeP2O7/carbon delivers superior rate capability and long-cycle stability for sodium ion batteries

Na2FeP2O7 cathode material exhibits great promise in sodium ion batteries (SIBs), due to its low cost and high structural durability. Nevertheless, the intrinsically poor electronic conductivity and sluggish Na+ diffusion kinetics of Na2FeP2O7 hinder its practical application. Herein, a synergistic cooperation of continuous amorphous carbon layer and optimized Co doping strategy is proposed to design high-performance SIB cathode (Co-doped Na2FeP2O7/C) via in-situ sol–gel method, where Co integration significantly enhances both the electronic conductivity and the Na+ diffusion kinetics, as confirmed by the combination of ex/in-situ characterizations and density functional theory calculations. Valuably, the synergy of amorphous carbon layer and appropriate Co doping restrains the structure stress to “zero-strain”, Which remains beneficial for 0.10Co-NFO@C to display a high capacity of 96.12 mAh g-1 at 0.05C and a high-rate capacity of 61.75 mAh g-1 at 60C with the capacity retention of 79.9% after 5000 cycles. Moreover, optimized Co-doped Na2FeP2O7/C also shows outstanding cycling performance and rate capability when assembled into full batteries (hard carbon as the anode), demonstrating a reversible capacity of ∼110.9 mAh g-1 at 50 mA g−1, and a respectable capacity retention of 78.0% at 500 mA g−1 for 500 cycles. The strategy inspires new advances towards zero-strained cathode materials for high performance SIBs.

Dual‐Carbon‐Coated Na2FeP2O7 Cathode Materials for Na‐Ion Batteries with Superior High‐Rate and Cycling Stability

The iron‐based pyrophosphate Na2FeP2O7 (NFP) is considered as one of the most promising cathodes for sodium‐ion batteries (SIBs) due to its low‐cost and superior structure stability, yet it usually suffers from poor intrinsic electronic conductivity. Herein, a two‐step carbon‐coating technique has been developed to synthesize high‐performance NFP@C cathode materials by controlling the NFP particle size and the coating layer uniformity. The first step of in‐situ carbon coating greatly restrains the excessive growth of NFP crystals with a shortened Na‐ion diffusion path. Meantime, the extra secondary carbon‐coating is adopted to repair some exposed areas, guaranteeing the full coverage of NFP particles for rapid electronic transfer. As a consequence, the as‐obtained NFP@C cathode delivers a high discharge capacity of 95.2 mAh g−1 at 0.1 C (theoretical value: 97 mAh g−1) and with high‐rate capability (75.2 mAh g−1 at 5 C) within 2.0–4.0 V. A capacity retention of 95.3% can be achieved even after 500 cycles at 5 C in coin‐type cells. Such superior electrochemical performances are expected to quickly promote the applications of NFP in SIBs.

3D Bismuth@N-Doped carbon microflowers for ultrahigh rate and stable sodium storage

Sodium-ion batteries (SIBs) are gaining attention in the energy storage market due to their high theoretical capacity and affordability. However, challenges such as volume expansion and sluggish dynamics during sodiation/desodiation hinder their practical application. A 3D bismuth@N-doped carbon microflowers (Bi@NC) anode was successfully prepared to address these issues. The Bi nanosheets expedite Na ions and electrons transport and inhibit particle pulverization, while the N-doped carbon layer maintains electrode stability and improves electronic conductivity. The Bi@NC anode exhibits ultrahigh rate (336.7 mAh/g at 20 A/g) and stable performance (92.9% capacity retention after 2500 cycles at 5 A/g).

Machine Learning Assisted Electronic/Ionic Skin Recognition of Thermal Stimuli and Mechanical Deformation for Soft Robots.

Soft robots have the advantage of adaptability and flexibility in various scenarios and tasks due to their inherent flexibility and mouldability, which makes them highly promising for real-world applications. The development of electronic skin (E-skin) perception systems is crucial for the advancement of soft robots. However, achieving both exteroceptive and proprioceptive capabilities in E-skins, particularly in terms of decoupling and classifying sensing signals, remains a challenge. This study presents an E-skin with mixed electronic and ionic conductivity that can simultaneously achieve exteroceptive and proprioceptive, based on the resistance response of conductive hydrogels. It is integrated with soft robots to enable state perception, with the sensed signals further decoded using the machine learning model of decision trees and random forest algorithms. The results demonstrate that the newly developed hydrogel sensing system can accurately predict attitude changes in soft robots when subjected to varying degrees of pressing, hot pressing, bending, twisting, and stretching. These findings that multifunctional hydrogels combine with machine learning to decode signals may serve as a basis for improving the sensing capabilities of intelligent soft robots in future advancements.

Stochastic density functional theory combined with Langevin dynamics for warm dense matter.

This study overviews and extends a recently developed stochastic finite-temperature Kohn-Sham density functional theory to study warm dense matter using Langevin dynamics, specifically under periodic boundary conditions. The method's algorithmic complexity exhibits nearly linear scaling with system size and is inversely proportional to the temperature. Additionally, a linear-scaling stochastic approach is introduced to assess the Kubo-Greenwood conductivity, demonstrating exceptional stability for dc conductivity. Utilizing the developed tools, we investigate the equationof state, radial distribution, and electronic conductivity of hydrogen at a temperature of 30000K. As for the radial distribution functions, we reveal a transition of hydrogen from gaslike to liquidlike behavior as its density exceeds 4g/cm^{3}. As for the electronic conductivity as a function of the density, we identified a remarkable isosbestic point at frequencies around 7eV, which may be an additional signature of a gas-liquid transition in hydrogen at 30000K.

Fast-Charging Carbon Fiber Structural Battery Electrodes Using an Organic Polymer Active Material

Abstract Structural batteries require electrodes with integrated energy storage and load-bearing properties. Adoption of structural batteries can lead to mass and volume savings in electrified transportation and aerospace applications by storing energy within the object’s structural elements. However, to date, active materials investigated in structural batteries exhibit poor rate capabilities at higher C-rates and even worse performance at lower temperatures due to diffusion limitations. Organic radical polymers are promising alternatives because they possess fast-charging properties and good cycling stability. In this work, we integrate an organic radical polymer with carbon fiber (CF) fabric, in which the polymer acts as the active cathode material and the CF fabric possesses excellent tensile strength, modulus and electronic conductivity. At 20°C, the structural cathodes exhibited a reversible capacity of 67 mAh g-1 at 1C-rate and an 88% capacity retention at 25C-rate. Further, these structural electrodes retained more than 50% of their performance at -10°C (versus 20°C). These electrodes were further examined in a full cell containing a graphite-based anode, demonstrating a pathway for utilizing redox-active polymer-based active materials in structural and fast-charging organic batteries.

Improved Thermoelectric Performance in Ga‐ and Te‐Co‐introduced Tetrahedrite Cu12Sb4S13

As an earth‐abundant, environment‐friendly, and cost‐effective material, tetrahedrite Cu12Sb4S13 has attracted much attention in thermoelectrics (TEs). However, the TE performance of the pristine Cu12Sb4S13 (CSS) is mediocre, thereby much improvement is required. In this work, both the electronic and phonon transports of the CSS are engineered using Ga2Te3 as a dopant. In the results, it is indicated that dual substitutions of Ga for Cu and Te for Sb not only cause the enhancement of power factor via electronic band structure tuning, but also leads to a drop in both the electronic and lattice thermal conductivities. As a result, the total thermal conductivity (κ) decreases to 0.98 W m−1 K−1 at 770 K, which is about 58% that of the pristine CSS, thus improving the TE performance with the highest dimensionless figure of merit value increasing to 0.95 for (Cu12Sb4S13)0.9(Ga2Te3)0.1 at 773 K, 1.9 times that of the pristine CSS (≈0.5 at 770 K).

Fluorinated Surface Engineering Towards High‐Rate and Durable Potassium‐Ion Battery

AbstractSolid electrolyte interphase (SEI) crucially affects the rate performance and cycling lifespan, yet to date more extensive research is still needed in potassium‐ion batteries. We report an ultra‐thin and KF‐enriched SEI triggered by tuned fluorinated surface design in electrode. Our results reveal that fluorination engineering alters the interfacial chemical environment to facilitate inherited electronic conductivity, enhance adsorption ability of potassium, induce localized surface polarization to guide electrolyte decomposition behavior for SEI formation, and especially, enrich the KF crystals in SEI by self‐sacrifice from C−F bond cleavage. Hence, the regulated fluorinated electrode with generated ultra‐thin, uniform, and KF‐enriched SEI shows improved capacity of 439.3 mAh g−1 (3.82 mAh cm−2), boosted rate performance (202.3 mAh g−1 at 8.70 mA cm−2) and durable cycling performance (even under high loading of ~8.7 mg cm−2). We expect this practical engineering principle to open up new opportunities for upgrading the development of potassium‐ion batteries.

Fluorinated Surface Engineering towards High-rate and Durable Potassium-ion Battery.

Solid electrolyte interphase (SEI) crucially affects the rate performance and cycling lifespan, yet to date more extensive research is still needed in potassium-ion batteries. We report an ultra-thin and KF-enriched SEI triggered by tuned fluorinated surface design in electrode. Our results reveal that fluorination engineering alters the interfacial chemical environment to facilitate inherited electronic conductivity, enhance adsorption ability of potassium, induce localized surface polarization to guide electrolyte decomposition behavior for SEI formation, and especially, enrich the KF crystals in SEI by self-sacrifice from C-F bond cleavage. Hence, the regulated fluorinated electrode with generated ultra-thin, uniform, and KF-enriched SEI shows improved capacity of 439.3 mAh g-1 (3.82 mAh cm--2), boosted rate performance (202.3 mAh g-1 at 8.70 mA cm-2) and durable cycling performance (even under high loading of ~8.7 mg cm-2). We expect this practical engineering principle to open up new opportunities for upgrading the development of potassium-ion batteries.

Facile synthesis of porous ZnCo2O4 micro–flower decorated with SWCNTs toward superior lithium storage performance

Binary metal oxides ZnM2O4 (A = Co, Fe, Mn) with spinel structures have been widely studied for their high theoretical specific capacity, relatively low cost, controllable morphology and synergistic effect between metal oxides with different charging and discharging mechanisms. However, the electrochemical properties are seriously affected by the huge volume change during cycles and poor electronic conductivity. In this work, porous ZnCo2O4 micro–flowers self–assembled from nano–sheets are successfully prepared by a simple solvothermal method followed by a heat treatment process without the aid of any soft/hard templates, and the resulting ZnCo2O4 active material is further decorated with SWCNTs. The phase composition, morphology characteristic, specific surface area, pore size distribution, elemental valence state and other information of the as–prepared samples are analyzed by relevant techniques such as XRD, FTIR, FESEM, (HR)TEM, TGA, Raman, N2 adsorption/desorption measurement and XPS. As anode materials in Li–ion batteries, the ZnCo2O4/SWCNTs product exhibits high charge/discharge specific capacity, excellent cycling stability and remarkable rate capability. Excellent electrochemical performance benefits from the special micro–/nano–structure characteristics of the as–synthesized ZnCo2O4/SWCNTs electrode material and good dynamic characteristics during cycling.

Investigating the influence of oxygen-functionalized graphene nanosheets as an efficient multifunctional material for supercapacitor and electrocatalytic water splitting applications

Graphene oxide (GO) has received great research attention to develop its efficiency in electrochemical applications, particularly supercapacitor (SC) and water splitting systems. However, the presence of various oxygen moieties in GO drastically reduces the utilization of the material for commercial usages. In this work, we demonstrate the use of different sources to reduce graphene oxide (GO) nanosheets. The partially reduced GO not only improves the electronic conductivity but also boosts the interaction between the sp2- and sp3-hybridized carbon atoms. Benefiting from the partial reduction process, RGO is applied for the SC test in the three-electrode system and reveals a specific capacitance of 151.1 F g−1 at 1 A g−1 with a long cycle life. Furthermore, the asymmetric solid-state device can also be constructed from an M-GO cathode with an activated carbon anode, which displays a specific capacitance of 54.4 F g−1 at 1 A g−1, with a maximum energy density of 19.3 W h kg−1. Besides, the electrochemical water splitting performance of the partially reduced GO in KOH solution was also explored, confirming the effectiveness of the reduction process. This work highlights the successful preparation of RGO nanosheets, which may open a new route to constructing high-performance energy storage and conversion devices.