Poor Electronic Conductivity Research Articles

Synergistically Boosted Na+ Migration and Deep Desodiation Stability of NASICON Cathode via High Entropy Regulation.

Mn-containing sodium superionic conductor (NASICON) compounds have shown considerable potential as cathode for sodium-ion batteries (SIBs) owing to higher working voltage (V5+/V4+: 3.9V), lower cost, and lower toxicity compared to full vanadium-based NASICON Na3V2(PO4)3. Taking Na3.3V1.7Mn0.3(PO4)3 (NVMP) as an example, its practical application is still restricted by poor electronic conductivity, sluggish intrinsic Na+ diffusion, and poor high-voltage stability. In this work, a high entropy strategy is proposed to develop Na3.3V1.613Mn0.3(Cr, Fe, Co, Ni, Zr)0.1(PO4)3 (HE-NVMP) cathode for not only enabling more and rapid Na+ migration but also significantly improving deep desodiation stability. Based on theoretical calculations and experimental findings, such high entropy modification can efficiently alter the coordination environments of both V/Mn and Na sites for reducing Na+ diffusion energy barrier, increasing the occupancy of Na+ at Na(2)sites, and consolidating the structure stability. Thus, the obtained HE-NVMP delivers superior high-rate capability (91.7 mAh g-1) up to 50 C and excellent cycling performance (capacity retention: 81.2%) after 10000 cycles at 20 C at the cutoff voltage of 4.1V. More importantly, such cathode also exhibits superior sodium storage properties at a higher cutoff voltage (4.5V) with electrochemical polarization with 75% reduction at 1 C and higher capacity retention of 80.3% after 2000 cycles at 20 C compared to pristine counterpart, indicating a great potential for practical rechargeable batteries with excellent overcharge resistance capability.

Progress and perspectives on electrocatalysis in room-temperature Na-S batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries that typically feature multielectron conversion chemistries can allow an ultrahigh specific capacity of 1675 mA h g-1 and a high energy density of 1275 W h kg-1 but unfortunately suffer from a lot of intractable challenges from sulfur cathodes. These issues cover the poor electronic conductivity of pristine sulfur and solid products, the severe shuttle effect of polysulfides, and the sluggish redox kinetics, etc. The shuttling behavior of polysulfides always leads to cathode/anode instability and performance degeneration. Recently, the emerging catalysis strategy has been demonstrated as a reliable pathway to tackle the central issues caused by sulfur electrochemistry and revitalize RT Na-S batteries. This review provides an overview of electrocatalysis in the realm of RT Na-S batteries. Sulfur conversion chemistries and critical challenges in RT Na-S batteries are generalized firstly. The emphasis is focused on discussing chemisorption mechanisms for polysulfides, material innovation of catalysts, selectivity and design of catalysts, and a series of catalysis regulation strategies. Finally, existing challenges and perspectives regarding catalysis in RT Na-S batteries are offered, with the aim of propelling its rapid development.

Trace Cu Doping Enabled High Rate and Long Cycle Life Sodium Iron Phosphate Cathode for Sodium-Ion Batteries.

Na4Fe3(PO4)2(P2O7) (NFPP) is currently receiving a lot of attention, as it combines the advantages of NaFePO4 and Na2FeP2O7 in terms of cost, energy density, and cycle stability. However, the issues of intrinsic poor electronic conductivity and difficult high-purity preparation may impede its practical application. Herein, the pivotal role of Cu doping in strengthening the polyanion structure and improving its electrochemical properties is comprehensively investigated. It is found that trace Cu doping not only expands the lattice volume of NFPP but also suppresses the formation of the inactive NaFePO4 impurity phase. In addition, Cu doping can effectively reduce the structural variations of NFPP during sodiation/desodiation processes (2.02%) while decreasing the band gap and lowering the ion mobility energy barrier (from 0.46 to 0.426 eV). Consequently, the Cu-doped NFPP electrode exhibits superior rate capability and long-term cycling performance. The computational simulations reveal a strong electronic interaction between Fe and Cu that tunes the electron localization and distribution, and additional Na+ transport channels can be created in NFPP by distorting the [PO4] units adjacent to the doping site, which provides a reference to enhance the performance of NFPP and reveals the great application potential of NFPP materials.

Organic molecular design for high-power density sodium-ion batteries.

Organic materials, with abundant resources, low cost, high flexibility, tunable structures, lightweight nature, and wide operating temperature range, are regarded as promising candidates for sodium-ion batteries (SIBs). Unfortunately, their poor electronic and ionic conductivity remain significant challenges, hindering the achievement of high power density for sodium storage. Power density, a critical factor in battery performance evaluation, is essential for assessing fast charging capabilities. Therefore, it is essential to summarize strategies for high-power density SIBs in further development. To address these limitations and guide future development, this highlight summarizes key advancements in SIB research over the past decade. We outline the effective molecular design strategies for improving high-power-density sodium storage, with a focus on structural optimizations ranging from the backbone to the side chains. Additionally, we propose future perspectives on electrodes, electrolytes, and potential applications to enhance the power density of organic sodium-ion batteries. This review is intended to give a comprehensive guideline on the future design of organic materials for fast-charge ability and overall performance.

Spherical Mg/Cu Co‐doped Na4Fe3(PO4)2P2O7 Cathode Materials with Mitigated Diffusion‐induced Stresses and Enhanced Cyclic Stability

Na4Fe3(PO4)2P2O7 (NFPP) has been regarded as the promising cathode material for sodium‐ion batteries (SIBs). However, the practical applications of NFPP are hindered by its high‐volume changes, poor intrinsic electron conductivity and sluggish Na+ ions diffusion kinetics. Herein, a spray‐drying and solid‐state reaction method have been utilized to fabricate the spherical trace amount Mg/Cu co‐doped Na4Fe3(PO4)2P2O7 (NFMCPP). The Mg/Cu co‐doping can effectively mitigate the lattice volume change and promote the electronic conductivity of NFMCPP by reducing band gap between the conduction and valence bands. While, the unique spherical structured NFMCPP with a carbon film even coated on its surface ensures rapid electron transport. Moreover, small NFMCPP particles with spherical geometry demonstrate an alleviated diffusion‐induced stress and enhanced structural stability, due to the high sphericity structure enables fluent Na+ extraction/insertion, leads to a low high‐stress concentration and uniform stress/strain distribution during extensive (de)sodiation process. Consequently, the optimized spherical NFMCPP cathode materials exhibit an excellent rate capability and cyclic stability.

High-Entropy and Na-Rich-Designed High-Energy-Density Na3V2(PO4)3/C Cathode.

The Na3V2(PO4)3 (NVP) cathode holds the merit of a stable 3D NASICON structure for ultrafast Na+ diffusion, yet it is still confronted with poor electronic conductivity (10-9 S cm-1) and insufficient energy density (∼370 W h kg-1). Herein, a series of high-entropy-doped Na3+xV1.76-xZnx(GaCrAlIn)0.06(PO4)3 (x = 0, 0.2, 0.35, and 0.5) cathodes are systematically prepared with an activated V5+⇌V4+ high-voltage plateau (4.0 V) and elevated discharge capacity, which is derived from the charge compensation of divalent Zn substituting for trivalent V accompanied by extra Na+ input to create an Na-rich phase. A range of in situ/ex situ characterization studies and DFT calculations radically verify the charge conservation mechanism, enhanced bulk conductivity, and robust structural stability. Accordingly, in half-cells, the optimized cathode (x = 0.35) is capable of giving a much-improved discharge capacity (126.8 mA h g-1), reliable cycling stability (97.4%@5000 cycles@40 C), and a competitive energy density (426.1 W h kg-1) at 2.0-4.3 V. Upon reducing the discharge cutoff voltage to 1.4 V, the three-electron reaction (V5+⇌V2+) is entirely activated with superior stability, delivering an unparalleled capacity of 193.4 mA h g-1 with higher energy density (544.3 W h kg-1). Besides, it displays high capacity (126.1 mA h g-1) and energy density (417.2 W h kg-1) in NVPZGCAI-35//hard carbon full-cells at 1.6-4.1 V. Hence, this pioneering high-entropy and Na-rich strategy is above rubies for developing high-energy-density and high-stability sodium-ion batteries.

Cation‐Vacancy‐Induced Reinforced Electrochemical Surface Reconstruction on Spinel Nickel Ferrite for Boosting Water Oxidation

AbstractSpinel oxides still exhibit unsatisfactory electrocatalytic performance toward oxygen evolution reaction (OER) given their low intrinsic activity, poor electronic conductivity, and limited exposure of reaction sites. Defect engineering has garnered intensive attention and become a promising strategy to enhance the reaction kinetics. In this work, spinel NiFe2O4 nanospheres with rich nickel vacancies are prepared via simple one‐pot hydrothermal synthesis. Combined electrochemical measurements and in situ Raman characterization prove that a relatively higher degree of electrochemical surface reconstruction is realized after the introduction of nickel vacancies in NiFe2O4, in addition to boosted OER electrocatalytic performance. Further theoretical calculations also reveal that the cation‐vacancy‐induced effect can reduce the difficulty for surface reconstruction by increasing the octahedral nickel‐oxygen covalency in nickel ferrite. Contributed to the great structural flexibility and optimized electronic structure of the pre‐catalyst, the reconstructed electrocatalyst presents desirable OER performance, accompanied by long durability in alkaline solution. This work provides a sound strategy to intensify surface reconstruction on spinel oxides and design electrocatalysts with high efficiency toward water oxidation.

Rational Design of Porous Y2O3-MnOx/Carbon Heterostructures with Abundant Oxygen Vacancies for High-Efficiency and Ultrastable Zinc-Ion Storage.

Manganese oxides have been considered as the most competitive cathode materials for aqueous zinc-ion batteries (ZIBs) on account of their inherent safety, high operating voltage, environmental friendliness, and cost-effectiveness. Unfortunately, the manganese dissolution, inherently poor electronic conductivity, and the sluggish reaction kinetics of commercial manganese-based oxides severely hinder their practical applications. To address the above issues, we creatively developed hierarchical porous Y2O3-MnOx/C nanorods (named OV-YMO/C) with unique heterostructures and abundant oxygen vacancies via a facile MOF-assisted synthetic process and employed as the advanced cathode. Owing to the well-constructed porous structure, larger surface areas, abundant oxygen vacancies, and strong synergetic coupling effect at the heterogeneous interface, the as-obtained OV-YMO/C cathode exhibited a fascinating discharge capacity of 389.6 mAh g-1 at 0.1 A g-1. Simultaneously, it demonstrated remarkable rate performance (233 mAh g-1 at 4.0 A g-1) and cycling durability (90.6% capacity retention over 3000 cycles at 4.0 A g-1). The fabricated Zn//OV-YMO/C pouch cell could deliver superior flexibility and electrochemical stability under extreme bending conditions. Furthermore, the electrochemical reaction mechanism was comprehensively explored by kinetic analysis and density functional theory (DFT) calculations. The synergistic strategy by subtly combining the MOF-assisted approach, heterojunction engineering, and oxygen defects engineering provides valuable insights into the construction of cathode materials for high-rate and ultrastable aqueous ZIBs.

Carbon-Coated Coaxial Cable-like ZnO@SiO2@C for High-Performance Lithium-Ion Battery Anode Materials.

The practical applications of SiO2 anode material are limited by large volume changes and poor electronic conductivity. To reduce the effects of these problems, a carbon-coated coaxial cable-like ZnO@SiO2@C composite material was prepared. ZnO has a certian electronic conductivity and an electrochemical activity, and the carbon layer can alleviate the volume variation of SiO2, effectively improving the electronic conductivity and structural stability. At the same time, the carbon layer acts as a barrier to prevent direct contact between SiO2 and the electrolyte, thus promoting the formation of stable solid electrolyte interface films. Carbon-coated coaxial cable-like ZnO@SiO2@C exhibits excellent electrochemical properties, with a discharge specific capacity of 480.3 mAh g-1 after 500 cycles at a current density of 1 A g-1. The carbon-coated coaxial cable-like structure presents a potential application for alloying anode materials.

Insights on Prussian Blue Analogue Cathode Material Engineered with Polypyrrole Surface Protection Layer for Aqueous Rechargeable Zinc Metal Battery.

One of the key intricacies against using Prussian blue analogues (PBAs)in aqueous batteries is their gradual dissolution in aqueous electrolytes, resulting in inadequate cycling stability. Besides, the rate capability of PBAs is limited due to their poor electrical conductivity. To overcome these challenges, it is essential to tune the physical and chemical properties of PBAs at the nano regime without affecting the inherent charge storage properties, especially at high-voltage operating conditions. Through this work, a strategy is demonstrated to enhance the electrochemical performance of vanadium-based PBA (V-PBA) by surface engineering using a conducting polymer nano-skin (V-PBA/PPy) for aqueous zinc metal batteries. The polypyrrole (PPy) nano-skin over the V-PBA nanoparticles acts as an electron percolation path to ameliorate the poor electronic conductivity of the otherwise pristine V-PBA. Interestingly, the V-PBA with an optimized polypyrrole coating (V-PBA/PPy-2) exhibits an enhanced specific capacity (173 mAh g-1 at 0.10 A g-1) than the pristine V-PBA counterpart (80 mAh g-1) and 85% capacity retention up to 500 cycles. The DFT calculation confirms the synergistic interaction between PPy and V-PBA and the presence of PPy favors the adsorption of Zn.

Two-Dimensional Porphyrin-Based Covalent Organic Frameworks/g-C3N4 Composites as High-Performance Supercapacitor.

Covalent organic frameworks (COFs) with high porosity and redox-active properties have been advanced as electrode materials for energy storage systems, although poor electron conductivity and inaccessibility of active pore sites hinder their performance as electrode material for supercapacitor application. Thus, incorporation of a COF with various conductive materials can be an effective strategy to improve their electrochemical performances for supercapacitors. Herein, we report the synthesis of POR-COF@g-C3N4 composites by fabricating a porphyrin-based COF on g-C3N4 via in situ solvothermal conditions. A series of COF composites, known as POR-COF@g-C3N4-X, were prepared by incorporating different ratios of COF (X = 10%, 20%, 30%, and 40%) into g-C3N4 and investigated as electrode materials for supercapacitor performance. The optimized COF composite (POR-COF@g-C3N4-30) achieved a specific capacitance of 788 F g-1 at 4 A g-1, much higher compared to pristine COF. Further, the asymmetric device assembled using POR-COF@g-C3N4-30 demonstrated a high energy density of 24.4 Wh kg-1 at a power density of 1152 W kg-1 and a long-term cycling life of 74% capacity retention after 6000 cycles. Our work highlights the scope of COF-based composites as active electrode materials for highly efficient supercapacitor performance.

Design and Manufacturing of Cost-Effective Water Electrolyzers at Industrial Current Densities Via an Ink-Free Integrated Dual Electrode Assembly

The clean and sustainable “green hydrogen” is highly attractive as an alternative energy.[1] However, the excessive cost of “green hydrogen” hinders its large-scale application, which is limited by the costly membrane electrode assembly (MEA) in proton exchange membrane electrolyzer cells (PEMECs).[2, 3] Conventional MEA fabrication involves numerous complex ink processes, resulting in a relatively high manufacturing costs. In addition, the ink-formed catalyst layers usually have poor electron conductivity and relatively large thickness, which causes significant catalyst underutilization.[3, 4] To simplify the manufacturing and increase the catalyst utilization, we revolutionize the conventional MEA via a facile ink-free and cost-effective integrated dual electrode assembly (IDEA) for reducing the costs and enhancing the performance of PEMECs. IDEA not only greatly simplifies fabrication processes of MEAs from over ten steps to three steps but also significantly increases hydrogen production rate simultaneously (45.26% more hydrogen at 1.8 V). Benefiting from the nano-thick catalyst layers, the IDEA can achieve an industrial “overload” current density of 6 A/cm2 at a low cell voltage of 1.82 V with an 83.9% noble catalyst saving, which outperforms most reported PEMECs. Particularly, the degradation rate of IDEA is only 24 μV/h at 1.8 A/cm2. References Pivovar, B., N. Rustagi, and S. Satyapal, Hydrogen at scale (H2@ Scale): key to a clean, economic, and sustainable energy system. The Electrochemical Society Interface, 2018. 27(1): p. 47.Ding, L., et al., Electrochemically grown ultrathin platinum nanosheet electrodes with ultralow loadings for energy-saving and industrial-level hydrogen evolution. Nano-Micro Letters, 2023. 15(1): p. 144.Mo, J., et al., Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting. Science advances, 2016. 2(11): p. e1600690.Yang, G., et al., Role of electron pathway in dimensionally increasing water splitting reaction sites in liquid electrolytes. Electrochimica Acta, 2020. 362: p. 137113. Figure 1

Investigating Cathode Ionomer Content and Assembly Techniques for Anion Exchange Water Electrolysers

An ionomer is often used in catalyst layers to a) adhere catalysts to the membrane or transport layer, b) facilitate ionic conductivity for OH- species through catalyst layers, and c) achieve ideal catalyst dispersions in catalyst inks used in spraying methods[1]. The choice of ionomer plays a crucial role in determining ion conductivity, water management, and mechanical stability within the membrane electrode assembly of anion exchange membrane water electrolysers (AEMWEs). Therefore, optimizing ionomer properties is crucial to achieving high-performance AEMWEs with efficient hydroxide transport.Both low and high ionomer loadings can lead to challenges in charge transport resistance. At low loadings, poor electronic conductivity and reduced contact between the catalyst layer and the membrane surface can occur due to a rough electrode interface[2]. This can result in inefficient charge transfer kinetics and hinder the overall efficiency (Figure 1c). Conversely, high ionomer loadings can lead to increased charge transport resistance, attributed to decreased gas permeability to the catalyst surface. The excessive presence of ionomer within the catalyst layer can block gas-liquid transport pores inside catalyst aggregates, limiting mass transport of reactants to the active sites[2]. This phenomenon can impede gas diffusion and oxygen reduction kinetics, leading to decreased performance and lower efficiency in AEMWEs (Figure 1d). Achieving an optimal ionomer loading balance is therefore essential for promoting efficient charge transfer and gas transport processes (Figure 1e), ultimately enhancing the overall performance and durability of AEMWE devices. The use of a proton conducting ionomer such as Nafion seems counterintuitive for use within AEMWEs, its hydroxide conductivity is comparatively lower, potentially limiting electrolyser performance. However, compared to Nafion, OH- conductive binders (Sustainion and PiperION) typically yield poorer electrodes, with larger catalyst aggregates[3].Two anion exchange ionomers and one ion exchange ionomer are evaluated across a range of loadings, and two different cathode assembly techniques, Catalyst coated substrates (CCS) and catalyst coated membranes (CCM) (Figure 1a). Since different catalyst surfaces are observed to influence ionomer degradation differently[4], commercially available Pt/C was utilised as a catalyst to focus on ionomer content and fabrication techniques. To investigate the effect of using hydrophobic or hydrophilic ionomers on catalyst layer homogeneity, the content of Nafion, Sustainion, and PiperION ionomers in the catalyst layers was varied (Figure 1b). Electrochemical impedance spectroscopy was used to determine the trade-off between high and low ionomer contents, polarisation curves found the in-situ electrocatalytic performance and highlighted the best performing ionomer and fabrication technique. Scanning electron microscopy was used to highlight the differences in catalyst layer structures and homogeneity.[1] Volk et al. Nov. 2023, EES. Catal. 2(1). 109-137. DOI: 10.1039/D3EY00193H.[2] Zhao et al. Feb. 2023, Int. J. Hydrogen Energy. 48(13). 5266-5275. DOI: 10.1016/j.ijhydene.2022.11.057.[3] Jervis et al. Nov. 2017, J. Electrochem. Soc. 164(14). 1551-1555. DOI: 10.1149/2.0441714jes.[4] Li et al. Mar. 2019, ACS Appl. Mater. Interfaces. 11(10). 9696–9701. DOI: 10.1021/acsami.9b00711.Figure 1: Schematic illustrations of: a) Membrane electrode assembly fabrication techniques, catalyst coated membrane and catalyst coated substrate. b) The chemical structures of PiperION A5 by Versogen, Sustainion XA-9 by Dioxide Materials, and Nafion by Liquion. c) Catalyst layer with low ionomer loading. d) Catalyst layer with moderate ionomer loading. e) Catalyst layer with high ionomer loading. Figure 1

(Invited) Extrinsic and Intrinsic Methods to Increase the Rate Performance of MnO2 Electrodes

MnO2 is one of the most well studied pseudocapacitive material for aqueous supercapacitors owing to the surface and near surface-confined redox processes. However, due to its poor electronic conductivity, a large amount of conducting additive, needs to be added to achieve high-rate charge storage. Since the conducting additive does not contribute much to the specific capacitance, this leads to decrease in total energy density of the cell in terms of both mass and volume. In addition, polymeric binders are also necessary to fabricate rigid electrode with good contact.As an alternative to these typical conductive binders and polymer binders, we have studied the possibility of using RuO2 nanosheets as a novel inorganic binder with polymeric properties, high electronic conductivity and excellent pseudocapacitive properties. For example, by adding a small amount of RuO2 nanosheets to particulate MnO2, a large synergetic effect is observed leading to a high utilization of MnO2 pseudocapacitance.1 The optimized amount of RuO2 in the composite was 13 wt%, which is much lower than the amount generally used for conductive carbon additives. The size of nanosheet binders also affects the properties of the electrode. Using MnO2 nanosheets and RuO2 nanosheets with different lateral sizes, it has been shown that larger sized nanosheets affords better conductive binder properties through a better electronic conduction network structure.Asides from using conductive binders, heterogeneous doping can increase the intrinsic conductivity of MnO2. We have shown that Ir-doped Birnessite shows faster redox behavior than pristine MnO2 and this enhanced kinetics are reflected on the exfoliated nanosheets. These properties can be discussed based on the electronic interaction between Mn and Ir.The pseudocapacitive performance of MnO2 can also be manipulated by inducing cationic defects in Birnessite. Low temperature annealed MnO2 with higher number of defects shows higher specific capacitance at low rate, albeit at the loss of high-rate performance. This trade-off is discussed based grain-boundary resistance dominating the rate performance. Acknowledgments This work was supported in part by ISHIFUKU Metal Industry Co., Ltd. and a Japan Science and Technology Agency Program on Open Innovation Platform with Enterprises,Research Institute and Academia (JST OPERA JPMJOP1843).

Impact of Mixed Salt Electrolytes for LiMnxFe1-XPO4/Graphite Li-Ion Cells

Lithium Manganese Iron Phosphate, LiMnxFe1-xPO4, (LMFP), is a promising positive electrode material for Lithium-ion batteries. Introduced by Pahdi et al. in 1997 [1], it is an alternative to the high-cost Nickel Manganese Cobalt (NMC) layered oxides and the low energy density Lithium Iron Phosphate (LFP) positive electrode materials. The LMFP material has a higher operating voltage than LFP, shows good cyclability, is low cost, and has a stable structure. However, the LMFP material suffers from poor rate capability due to its poor electronic conductivity and poor ionic diffusion. This hampers its use for high C-rate applications. Tailoring electrolytes to ensure better ionic diffusion at the solid/electrolyte interface is one solution to improve rate capability of these LMFP cells. Herein, we study the effect of different salts and mixed salts on LMFP/graphite Li-ion pouch cells and come up with a suitable electrolyte combination for LMFP cells. The salts used in this study are readily available salts and the mixed salts were made with a combination of these readily available salts at different ratios. The tests were conducted in a 70 °C temperature box to accelerate failure in these cells, as a method to screen these salts/mixed salts. Our observations show that mixed salts play a significant role in improving the lifetime of these cells, with the best cell reaching the end of life (EOL) after ~280 cycles at 70 °C. As LMFP is prone to manganese dissolution, the amount of manganese deposited on the negative electrode was quantified using X-ray Fluorescence spectroscopy (XRF). The cells using mixed salts display a lower amount of manganese deposited on the graphite compared to the individual salts. The use of readily available mixed salt electrolytes seems to improve cycle life, which is promising for the future commercialization of the LMFP positive electrode Li-ion cells.

Factorial optimisation of CoCuFe- LDH/graphene composites for water splitting

The increasing energy demand, driven by industrialization and global population growth, has increased the focus on developing clean and sustainable energy sources [1]. Hydrogen (H2) has emerged as a promising alternative to carbon-based fuels due to its low cost, higher calorific value, and absence of pollution emissions [2]. Electrochemical water splitting has recently gained prominence as a highly attractive technique for efficient hydrogen production [3]. Therefore, the development of efficient and cost-effective catalysts for the hydrogen evolution reaction (HER) is crucial for advancing energy conversion and storage technologies [2]. The layered double hydroxides (LDHs) have emerged as promising non-noble metal catalysts for HER due to their unique composition and structural features, making them efficient and stable catalysts [4]. Indeed, copper (Cu)-based materials exhibit high electrical conductivity, the CuFe-LDH has been reported as an interesting electrocatalyst since iron (Fe) can enhance the reactivity in the HER process [5]. Likewise, cobalt (Co)-based catalysts emerge as potential alternatives to noble-metal catalysts in water-splitting applications, attributed to the high redox potential of Co species, cost-effectiveness, and stability in both acidic and basic environments [6]. Moreover, in binary LDHs, introducing a third metal ion has been shown to change the electronic structure and improve conductivity; hence, providing more active sites and facilitating a fast electron transfer process [7]. However, the LDHs as electrocatalysts are limited by their poor electronic conductivity and tendency for agglomeration. On the other hand, graphene (G), a single layer of carbon atoms arranged in a hexagonal lattice, serves as an excellent supporting matrix for LDHs due to its exceptional electronic conductivity and high surface area, facilitating efficient electron transfer during the water-splitting reaction [8]. Therefore, in this work, CoCuFe-LDH composites were synthesised and grown on graphene through a cost-effective and straightforward one-step hydrothermal process. Experiments were conducted to assess the electrocatalytic properties of the trimetallic CoCuFe-LDH/G and its binary counterparts to investigate how each component affected the electrochemical performance and HER activity. The onset potential and Tafel slope were selected as the basis for characterising the catalytic performance of the materials. The linear sweep voltammetry (LSV) curves of CoCuFe-LDH/G composites for HER are shown in Figure 1. It can be observed that the trimetallic Co[1.5]Cu[3]Fe[3]-LDH/G[10] shows the lowest onset potential at -0.39 V with a Tafel slope of 76.58 mV dec-1, compared to its binary counterparts. While CuFe-LDH/G shows the highest onset potential (-0.52 V) and Tafel slope (115.56 mVdec-1), indicating that Co plays an important role in the HER performance. Furthermore, the trimetallic composite demonstrated favourable electronic properties, with a charge transfer resistance (RCT) of 486.6 Ω, and exhibited good stability without significant loss of catalytic activity over 24 h. Therefore, this study provides a facile and efficient strategy to design a trimetallic LDH electrocatalyst combined with graphene, demonstrating that the conductive nanoflake structure established by graphene provides a sufficient electron supply to the composite during the electrocatalytic process, enhancing the HER activity.

Large Particle LiFePO4for High Energy Applications

Lithium-ion batteries (LIBs) are the primary sources of power for electric vehicles (EVs), consumer electronics, and grid storage applications.1 However, the widespread usage of LIBs in sectors like EVs and grid storage still presents challenges in terms of cost reduction, minimized environmental impact, and enhanced sustainability. In order to tackle the issue of high cost and increased environmental impact, there is significant emphasis on olivine structured LiFePO4 (LFP) over other common cathode chemistries (i.e., NMC, LCO & LNO) because of its lower cost and environmental friendliness resulting from the abundance of iron.2,3 LFP also possesses desirable properties including high thermal stability and cycle life. Nevertheless, in comparison to layered oxides, LFP materials faces issues of poor electronic conductivity and low Li+ ion diffusion, which have been mitigated through the reduction of particle sizes to submicron (500-800 nm) and the implementation of carbon coating methods.4,5 Recently, we have made notable progress in enhancing the energy density LFP based cathodes.6 This accomplishment was achieved by combining mechanofusion processing and impact milling to consolidate submicron particles into ~10 μm dense flakes using a dry process known as dry particle flaking (DPF). In this presentation, DPF processing will be further demonstrated. Dense ~10 μm LFP/C flake composites with a high packing fraction and a low surface area will be described that; allow ultra high density (UHD) electrodes to be fabricated with electrode press densities exceeding 3.0 g/cm3. These electrodes are fabricated with high loadings (17 mg/cm2) and electrode formulations comprising 96% LFP active material. This corresponds to an electrode porosity of just 8%, resulting in a remarkable 44% increase in volumetric energy density compared to conventional LFP with electrode formulations consisting of 90% active material, as shown in Figure 1(a). In addition, as shown in Figure 1(b), improved cycling retention was observed for UHD LFP coatings compared to conventional LFP with identical columbic efficiency. Moreover, voltage polarization is also reduced for UHD LFP coatings compared to conventional LFP, as shown in Figure 1(c). The capability to manufacture immensely dense LFP electrodes could have significant implications, as it enables the production of cost-effective and environmentally friendly Li-ion cells, while achieving high volumetric energy densities approaching that of Li-ion cells employing layered oxide cathodes. References : (1) Wang, J.; Shen, Z.; Yi, M. Hydraulic Compaction on Electrode To Improve the Volumetric Energy Density of LiFePO 4 /Graphite Batteries. Ind. Eng. Chem. Res. 2019, 58 (34), 15407–15415. https://doi.org/10.1021/acs.iecr.9b01530.(2) Ren, X.; Li, Z.; Zheng, Y.; Tian, W.; Zhang, K.; Cao, J.; Tian, S.; Guo, J.; Wen, L.; Liang, G. High Volumetric Energy Density of LiFePO 4 Battery Based on Ultrasonic Vibration Combined with Thermal Drying Process. J. Electrochem. Soc. 2020, 167 (13), 130523. https://doi.org/10.1149/1945-7111/abba64.(3) Lin, Y.; Gao, M. X.; Zhu, D.; Liu, Y. F.; Pan, H. G. Effects of Carbon Coating and Iron Phosphides on the Electrochemical Properties of LiFePO4/C. Journal of Power Sources 2008, 184 (2), 444–448. https://doi.org/10.1016/j.jpowsour.2008.03.026.(4) Lu, W.; Jansen, A.; Dees, D.; Henriksen, G. Olivine Electrode Engineering Impact on the Electrochemical Performance of Lithium-Ion Batteries. J. Mater. Res. 2010, 25 (8), 1656–1660. https://doi.org/10.1557/JMR.2010.0214.(5) Ahsan, Z.; Ding, B.; Cai, Z.; Wen, C.; Yang, W.; Ma, Y.; Zhang, S.; Song, G.; Javed, M. S. Recent Progress in Capacity Enhancement of LiFePO4 Cathode for Li-Ion Batteries. Journal of Electrochemical Energy Conversion and Storage 2021, 18 (1), 010801. https://doi.org/10.1115/1.4047222.(6) Syed, M. A.; Salehabadi, M.; Obrovac, M. N. High Energy Density Large Particle LiFePO 4. Chem. Mater. 2024,36 (2), 803–814. https://doi.org/10.1021/acs.chemmater.3c02301. Figure 1

Complex Charge Transport of Carbon Network in Composite Cathode for Solid-State Batteries

Constructing a well-defined electronic, ionic transport network is crucial for designing composite cathodes in solid-state batteries (SSBs). Despite the necessity of balancing conductivities within the electrode, higher energy density cathodes with rich active materials content (> 90 wt%) often result in electronically sufficient but ionically insufficient conduction. Despite this, adding carbonaceous conducting agents in this electrode design of SSBs was typically overlooked as a compromise of poor electronic conductivity, which should not be necessary according to the previous understanding. However, adding of carbon conducting agents often shows better electrochemical behaviors in SSBs. Therefore, we investigated the percolating mechanism of carbon additive, typically aiming to provide a sufficient electronic transport network in the composite cathodes. It was revealed that carbon nanofiber (CNF) maximized the utilization of cathode by connecting the electrically isolated cathode particles in the electronic transport limited system, and it conducts ions in the ionic transport limited system. This mixed ion and electronic conducting property of CNF enables the efficient transport network in the electrode, and it can establish high energy density and high power density composite electrodes. This study provides an understanding of the complex charge transport mechanism through CNF in the composite cathode and also suggests insights into the composite cathode design logic regarding of the percolation network.

Polypyrrole employed interfacial engineering of porous NiFe2O4/Ti3C2Tx hybridized triphasic freestanding films for high-performance flexible pseudocapacitors

Rational design of a unique hybrid derived from transition-metal oxides, possessing high capacity but poor electronic conductivity, with two-dimensional (2D) MXenes, owning metallic conductivity but limited capacity and instability in aqueous electrolytes, is expected to produce innovative electrode materials for supercapacitor. In this study, we fabricated a free-standing triphasic composite film of NiFe2O4 pillared Ti3C2Tx encapsulated with polypyrrole (MNFx@PPy). This composite combined merits from large redox capacity of NiFe2O4 and high conductivity of Ti3C2Tx to operate within a voltage window of 1.2 V in 2.0 M H2SO4 electrolyte. The MNF10@PPy electrode had a specific capacity of 706.6 mAh·g−1 at 1.0 A·g−1, with 81.13 % retention at a high current density of 20 A·g−1. The integration of PPy enhanced interfacial contact of the components which leads to upsurge in electrochemical performance and stability of the tri-component system. When the fabricated asymmetric flexible supercapacitor (MXene@PPy//MNF10@PPy) was assessed with broad 1.6 V, a complimentary potential window of both electrodes, the device offered 37.49 Wh·kg−1 energy density at a power density of 3879 W·kg−1. This study underscores the synergetic potential of the MNF10@PPy composite to improve energy storage pseudocapacitive electrodes for flexible devices.

Electrospun Mesoporous Ni0.5Zn0.5Fe2O4 - CNT - Hollow Carbon Ternary Composite Nanofibers as High Performance Electrodes for Advanced Symmetric Supercapacitors.

Spinel ferrites have attracted considerable interest in energy storage systems due to their unique magnetic, electrical and catalytic properties. However, they suffer from poor electronic conductivity and low specific capacity. We have addressed this limitation by synthesizing composite hollow carbon nanofibers (HCNF) embedded with nanostructured Nickel Zinc Ferrite (NZF) and Multiwalled carbon nanotubes (CNT), through coaxial electrospinning. These ternary composite nanofibers NZF-CNT-HCNF have a high specific capacity of 833 C g-1 at a current density of 1 A g-1 and have a capacity retention of 90 % after 3000 cycles. Their performance is much better than pure NZF fibers (180 C g-1) or hollow carbon nanofibers (96 C g-1), suggesting synergy between various constituents of the composite. A symmetric supercapacitor fabricated from NZF-CNT-HCNF composite nanofibers (30 % NZF) has a high specific capacity of 302 C g-1 (302 A g-1) at a current density of 1 A g-1 and has a capacity retention of 95 % after 5000 cycles. At the same current density, the device has a high energy density of 39 Whkg-1 and power density of 1000 Wkg-1 at a current density of 1 A g-1. This performance can be attributed to the high specific surface area (776 m2 g-1), mesoporosity (pore size ~4 nm), interconnectedness of the nanofibers and high electrical conductivity of CNTs. These fibers can be used as light-weight high performance electrode materials in advanced energy storage devices.