Nanostructured Cathode Research Articles

Li2FeSiO4/C aerogel: A promising nanostructured cathode material for lithium-ion battery applications

Li2FeSiO4/C aerogel is successfully prepared using a high-temperature, high-pressure supercritical drying method. The prepared Li2FeSiO4/C aerogel is annealed at optimum temperature. The structural information is obtained from Powder X-ray diffraction and Fourier transform infrared spectroscopy results. The Li2FeSiO4/C aerogel annealing temperature is fixed at 700 °C based on the Thermogravimetric and differential scanning calorimetry. The electrical conductivity of the Li2FeSiO4/C aerogel is calculated using alternating current impedance, and it is 1.4738 × 10-8 S cm-1. The presence of carbon and the formation of Li2FeSiO4 is confirmed through Raman analysis. The X-ray photoelectron spectroscopy elemental analysis reveals Si4+, Fe2+, Li+, and C with their respective binding energies. Field emission scanning electron microscopy and transmission electron microscopy images show the formation of randomly distributed tiny particles are linked together within a porous structure. The specific surface area of 59.037 m2 g-1 with an average pore diameter of 22.8 nm is measured through N2 adsorption/desorption isotherm analysis. The electrochemical performance of the Li2FeSiO4/C aerogel exhibits a discharge capacity of 140 mA.h g-1 at 100 mA g-1 current density over 130 cycles with 100% coulombic efficiency. Lithium-ion diffusion co-efficient (DLi+ = 2.63 × 10-8 cm2 s-1) is measured from electrochemical impedance spectroscopy.

Theoretical analysis of efficiency for vacuum photoelectric energy converters with plasmon-enhanced electron emitter

Thermionic energy converters (TECs) convert heat or light into electrical energy based on electron emission in vacuum. By using a cathode consisting of metal nanostructures, plasmonic thermionic energy converters (PTECs) can overcome challenges concerning high operation temperature, which hinders the use of TEC for solar–thermal energy conversion. However, there is lack of theoretical analysis to describe the mechanism behind PTEC and to guide the design of device. In this study, we developed a simple model to calculate the power conversion efficiency of PTEC consisting of metal nanostructure cathodes, also named as vacuum photoelectric energy converter (VPEC) with plasmon-enhanced electron emitter, in this work. The distribution of plasmon-induced hot electrons was calculated using Fermi's golden rule. Under the assumption of ballistic transport and photoemission, the performance of VPEC was analyzed under different operating conditions. The results reveal that the size and shape of the nanostructure cathode influence the hot electron emission efficiency. For a cathode consisting of a single silver nanosphere, an optimal nanosphere diameter of ∼15 nm exists with optimal quantum efficiency and energy conversion of 8.71% and 1.88%, respectively, under the illumination of 339 nm light. Besides, the optimal performance for cathode consisting of a silver nanosphere array is ∼33% of that for the single silver nanosphere. This model provides insights into the dynamics of plasmon-induced hot electrons and guidelines for optimizing hot electron devices for photoelectric conversion applications.

Vacuum cold sprayed nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ as a high-performance cathode for porous metal-supported solid oxide fuel cells operating below 600 °C

Porous metal-supported solid oxide fuel cells (PMS-SOFCs) demonstrate potential to dramatically reduce their costs while simultaneously enhancing the durability of SOFCs. However, owing to the unsatisfactory performance improvement of PMS-SOFCs at low temperatures and available fabrication processes, their commercial applications are limited. In this study, exceptional performance of PMS-SOFCs for electricity generation at low temperatures (400–600 °C) with vacuum cold sprayed (VCS) nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) as the high-activity cathode, the plasma-sprayed Ce0.8Gd0.2O2−δ/La0.8Sr0.2Ga0.8Mg0.2O3−δ (GDC/LSGM) bilayer as the electrolyte, and a cermet consisting of the nickel–gadolinium-doped-ceria (Ni–GDC) composite as the anode. By carefully controlling the spray particle size, a nanostructured LSCF cathode is obtained, and the oxygen reduction reaction (ORR) is activated. Consequently, the microstructurally optimized cell exhibits remarkable peak power densities of >1 W/cm2 at 600 °C and >0.2 W/cm2 at 450 °C. Moreover, this nanostructured cathode maintains high activity over 1000 h at 550 °C due to the stable microstructure, strontium (Sr) surface segregation, and the exceptional stability of PMS-SOFCs. Our results demonstrate a simple route to dramatically improve the performance and stability of PMS-SOFCs operating at low temperatures by using a nanoscale cathode for activity toward the ORR.

Nanostructuring of Iron Disulfide Cathode Materials for Enhanced Thermal Batteries

For the U.S. Department of Defense, high-performance power sources are a critical technology for current and future gun-fired munitions. Molten salt thermal batteries are the reserve power source of choice for many weapon systems due to their high power density, proven long shelf life, and capability to function across a wide range of operating environments. The incorporation of nanomaterials into thermal battery components offers the potential to produce batteries with performance improvements, such as higher voltages at increased current densities. In this study, nanoscale iron disulfide (FeS2) was synthesized using a fully scalable, high energy milling method, and characterized utilizing SEM, XRD, ICP-OES, BET surface area analysis, TGA-DSC, and other techniques. Nanostructured cathode mixtures containing the nanoscale FeS2 and LiCl-KCl eutectic salt electrolyte were pressed into electrode pellets. Their electrochemical performance was then characterized as compared to standard FeS2 cathode electrode pellets currently used in industry. Single cell thermal battery discharge testing, polarization type scans, and pulse load capability were used to compare cell performance for better understanding of best-use applications for these materials. Compared to control cells, the cells utilizing nanostructured cathodes provided higher power response, with respect to both voltage and runtime.

‘Cotton-ball’ shaped porous iron-nickel sulfide: A high-rate cathode for long-life aqueous rechargeable battery

Aqueous rechargeable batteries (ARB) offer reasonably higher energy density and cycle life than their non-aqueous counterparts. Yet, the bottleneck is a limited choice of positive electrodes coupled with low-rate capability and inadequate cycle life. We report here a wet chemical approach to synthesize in-situ three-dimensional (3D) ‘cotton-ball’ shaped porous iron-nickel sulfide (FeNi2S4) (henceforth referred to as PINS) as a diffusion-controlled ARB electrode. It shows a high specific capacity of 177 mA h g−1 at 1 A g−1 vs Pt in the alkaline electrolyte with excellent rate capability (89 mA h g−1 at 40 A g−1) and ultra-long cycle life (10,000 cycles). Furthermore, a pouch-type full-cell ARB (FeNi2S4//AC) delivers an energy density of 56.7 Wh kg−1 at a power density of 871.5 W kg−1 with high cycling stability (10,000 cycles). The present study offers a straightforward and efficient approach for developing nanostructured transition metal sulfide-based cathode materials for practical ARB.

Zn-ion hybrid supercapacitors: Achievements, challenges and future perspectives

The newly-emerging Zn-ion hybrid supercapacitors (ZHSCs) are famed for their integration of high-capacity of Zn-ion batteries and high-power of supercapacitors (SCs), which are expected to meet the energy and power demands for both portable electronics and electrical vehicles. The practical application of ZHSCs faces serious challenges of achieving satisfactory energy density and developing suitable cathode materials and electrolytes. A systematic review on ZHSCs, the novel energy storage devices, is necessarily desired to spur the development of ZHSCs, but is still barren. This review provides a timely summary of recent advances on ZHSCs, and highlights the vital role of cathode materials and electrolyte systems in accelerating the prosperity of this kind of SCs. The ZHSCs fundamentals and the advanced engineering of various types of nanostructured cathode materials as well as their electrochemical characteristics and energy storage mechanisms are comprehensively discussed. The most recent development of electrolytes and Zn anode is also summarized and the effects of electrolyte compositions on the electrochemical performance of ZHSCs are elaborated. In the end, this review provides a detailed discussion about the existing critical challenges and presents future development perspectives on the favorable ZHSCs. This review provides a systematic summary of recent advances on ZHSCs including various types of cathode materials (carbon-based materials, conducting polymers, MXenes, TMOs), the most recent developed electrolyte systems, and their energy storage mechanisms. The existing critical challenges and a perspective to future development of favorable ZHSCs are provided. • A comprehensive summary of the techniques and the progress of ZHSCs is reviewed. • The fundamentals and recent developed cathode materials, electrolytes and anodes for ZHSCs are elaborated. • The existing critical challenges and a perspective to future development of ZHSCs are provided.

Understanding rapid charge and discharge in nano-structured lithium iron phosphate cathodes

A Doyle–Fuller–Newman (DFN) model for the charge and discharge of nano-structured lithium iron phosphate (LFP) cathodes is formulated on the basis that lithium transport within the nanoscale LFP electrode particles is much faster than cell discharge, and is therefore not rate limiting. We present some numerical solutions to the model and show that for relevant parameter values, and a variety of C-rates, it is possible for sharp discharge fronts to form and intrude into the electrode from its outer edge(s). These discharge fronts separate regions of fully utilised LFP electrode particles from those that are not. Motivated by this observation an asymptotic solution to the model is sought. The results of the asymptotic analysis of the DFN model lead to a reduced order model, which we term the reaction front model (or RFM). Favourable agreement is shown between solutions to the RFM and the full DFN model in appropriate parameter regimes. The RFM is significantly cheaper to solve than the DFN model, and therefore has the potential to be used in scenarios where computational costs are prohibitive, e.g. in optimisation and parameter estimation problems or in engineering control systems.

Progress and perspective of interface design in garnet electrolyte‐based all‐solid‐state batteries

AbstractInorganic solid‐state electrolytes (SSEs) are nonflammable alternatives to the commercial liquid‐phase electrolytes. This enables the use of lithium (Li) metal as an anode, providing high‐energy density and improved stability by avoiding unwanted liquid‐phase chemical reactions. Among the different types of SSEs, the garnet‐type electrolytes witness a rapid development and are considered as one of the top candidates to pair with Li metal due to their high ionic conductivity, thermal, and electrochemical stability. However, the large resistances at the interface between garnet‐type electrolytes and cathode/anode are the major bottlenecks for delivering desirable electrochemical performances of all‐solid‐state batteries (SSBs). The electrolyte/anode interface also suffers from metallic dendrite formation, leading to rapid performance degradation. This is a fundamental material challenge due to the poor contact and wettability between garnet‐type electrolytes with electrode materials. Here, we summarize and analyze the recent contributions in mitigating such materials challenges at the interface. Strategies used to address these challenges are divided into different categories with regard to their working principles. On one hand, progress has been made in the anode/garnet interface, such as the successful application of Li‐alloy anode and different artificial interlayers, significantly improving interfacial performance. On the other hand, the desired cathode/garnet interface is still hard to reach due to the complex chemical and physical structure at the cathode. The common methods used are nanostructured cathode host and sintering additives for increasing the contact area. On the basis of this information, we present our views on the remaining challenges and future research of electrode/garnet interface. This review not only motivates the need for further understanding of the fundamentals, stability, and modifications of the garnet/electrode interfaces but also provides guidelines for the future design of the interface for SSB.

Aluminum textile-based binder-free nanostructured battery cathodes using a layer-by-layer assembly of metal/metal oxide nanoparticles

Despite considerable interest in textile-based battery electrodes with large surface areas and mechanical flexibility, issues have restricted further advances in the energy performance of textile electrodes. These issues include the ineffective incorporation of conductive and/or active components into textile frameworks, the poor charge transfer between energy materials, and the formation of numerous unstable interfaces within textile electrodes. Herein, we introduce an aluminum textile-based lithium-ion battery cathode with remarkable areal capacity, high rate performance, and good cycling stability. Ligand exchange reaction-induced layer-by-layer (LbL) assembly of metal nanoparticles and small molecule linkers, with subsequent metal electroplating, perfectly converted polyester textiles to 3D-porous aluminum textiles that can be used as current collectors and high-energy reservoirs. The consecutive LbL assembly of high-energy LiFePO4 and conductive indium tin oxide nanoparticles onto the aluminum textiles using small organic linkers significantly increased the areal capacity and cycling stability (at least 580 cycles) of the resultant cathode, allowing facile charge transfer within the textile electrodes. Furthermore, the areal capacity of these textile electrodes increased from 1.07 to 3.28 mA h cm−2, with an increase in the folding number from 0 to 2.

Phenylphosphonate surface functionalisation of MgMn2O4 with 3D open-channel nanostructures for composite slurry-coated cathodes of rechargeable magnesium batteries operated at room temperature.

Spinel-type MgMn2O4, prepared by a propylene-oxide-driven sol–gel method, has a high surface area and structured bimodal macro- and mesopores, and exhibits good electrochemical properties as a cathode active material for rechargeable magnesium batteries. However, because of its hydrophilicity and significant water adsorption properties, macroscopic aggregates are formed in composite slurry-coated cathodes when 1-methyl-2-pyrrolidone (NMP) is used as a non-aqueous solvent. Functionalising the surface with phenylphosphonate groups was found to be an easy and effective technique to render the structured MgMn2O4 hydrophobic and suppress aggregate formation in NMP-based slurries. This surface functionalisation also reduced side reactions during charging, while maintaining the discharge capacity, and significantly improved the coulombic efficiency. Uniform slurry-coated cathodes with active material fractions as high as 93 wt% can be produced on Al foils by this technique employing carbon nanotubes as an electrically conductive support. A coin-type full cell consisting of this slurry-coated cathode and a magnesium alloy anode delivered an initial discharge capacity of ∼100 mA h g−1 at 25 °C.

Nanostructured Mn-based oxides as high-performance cathodes for next generation Li-ion batteries

Mn-based oxides have been regarded as a promising family of cathode materials for high-performance lithium-ion batteries, but the practical applications have been limited because of severe capacity deterioration (such as LiMnO2 and LiMn2O4) as well as further complications from successive structure changes during cycling, low initial coulombic efficiency (such as Li-rich cathode) and oxidization of organic carbonate solvents at high charge potential (such as LiNi0.5Mn1.5O4). Large amounts of efforts have been concentrated on resolving these issues towards practical applications, and many vital progresses have been carried out. Hence, the primary target of this review is focused on different proposed strategies and breakthroughs to enhance the rate performance and cycling stability of nanostructured Mn-based oxide cathode materials for Li-ion batteries, including morphology control, ion doping, surface coatings, composite construction. The combination of delicate architectures with conductive species represents the perspective ways to enhance the conductivity of the cathode materials and further buffer the structure transformation and strain during cycling. At last, based on the elaborated progress, several perspectives of Mn-based oxide cathodes are summarized, and some possible attractive strategies and future development directions of Mn-based oxide cathodes with enhanced electrochemical properties are proposed. The review will offer a detailed introduction of various strategies enhancing electrochemical performance and give a novel viewpoint to shed light on the future innovation in Mn-based oxide cathode materials, which benefits the design and construction of high-performance Mn-based oxide cathode materials in the future.

Enhancing nanostructured nickel-rich lithium-ion battery cathodes via surface stabilization

Layered, nickel-rich lithium transition metal oxides have emerged as leading candidates for lithium-ion battery (LIB) cathode materials. High-performance applications for nickel-rich cathodes, such as electric vehicles and grid-level energy storage, demand electrodes that deliver high power without compromising cell lifetimes or impedance. Nanoparticle-based nickel-rich cathodes seemingly present a solution to this challenge due to shorter lithium-ion diffusion lengths compared to incumbent micrometer-scale active material particles. However, since smaller particle sizes imply that surface effects become increasingly important, particle surface chemistry must be well characterized and controlled to achieve robust electrochemical properties. Moreover, residual surface impurities can disrupt commonly used carbon coating schemes, which result in compromised cell performance. Using x-ray photoelectron spectroscopy, here we present a detailed characterization of the surface chemistry of LiNi0.8Al0.15Co0.05O2 (NCA) nanoparticles, ultimately identifying surface impurities that limit LIB performance. With this chemical insight, annealing procedures are developed that minimize these surface impurities, thus improving electrochemical properties and enabling conformal graphene coatings that reduce cell impedance, maximize electrode packing density, and enhance cell lifetime fourfold. Overall, this work demonstrates that controlling and stabilizing surface chemistry enables the full potential of nanostructured nickel-rich cathodes to be realized in high-performance LIB technology.

Parametric study on electrodeposition of a nanofibrous LaCoO3 SOFC cathode

Solid oxide fuel cells (SOFCs) capable of operating at low to intermediate temperatures (600–750 °C) are vital for the development of robust SOFC power generation systems. In this regard, the oxygen reduction reaction is the rate-limiting step that requires new highly active catalysts or drastic improvements in the cathode microstructure when using the conventional cathode materials. Here, we report a parametric study on electrodeposition for synthesizing nanostructured cathodes for the SOFCs by producing a nanofibrous LaCoO3 cathode. The synthesis of the nanofibrous LaCoO3 involves preparing an electrically conductive template of carbon nanotubes onto the walls of a porous scaffold made of oxide-ion-conducting material followed by co-electrodeposition of La and Co hydroxides from an aqueous mixed-metal nitrate solution. Then, the deposited metal hydroxides are thermally converted to the LaCoO3 perovskite phase through low-temperature calcination performed at 800 °C. LaCoO3 microstructure is optimized as a function of deposition time, applied current, and solution concentration to obtain a nanofibrous morphology. Anode-supported SOFCs with the nanofibrous LaCoO3 cathode are tested for their electrochemical performance and durability. A durable performance obtained during the 200 h stability tests, performed at 750 and 800 °C and under a galvanostatic load of 1 A cm−2, shows the potential of the electrodeposition for producing robust nanostructured SOFC cathodes.

Improved Field Emission Properties of Carbon Nanostructures by Laser Surface Engineering.

We herein present an alternative geometry of nanostructured carbon cathode capable of obtaining a low turn-on field, and both stable and high current densities. This cathode geometry consisted of a micro-hollow array on planar carbon nanostructures engineered by femtosecond laser. The micro-hollow geometry provides a larger edge area for achieving a lower turn-on field of 0.70 V/µm, a sustainable current of approximately 2 mA (about 112 mA/cm2) at an applied field of less than 2 V/µm. The electric field in the vicinity of the hollow array (rim edge) is enhanced due to the edge effect, that is key to improving field emission performance. The edge effect of the micro-hollow cathode is confirmed by numerical calculation. This new type of nanostructured carbon cathode geometry can be promisingly applied for high intensity and compact electron sources.

Fast Heat Transport Inside Lithium-Sulfur Batteries Promotes Their Safety and Electrochemical Performance.

SummaryLithium-sulfur batteries are paid much attention owing to their high specific capacity and energy density. However, their practical applications are impeded by poor electrochemical performance due to the dissolved polysulfides. The concentration of soluble polysulfides has a linear relationship with the internal heat generation. The issue of heat transport inside lithium-sulfur batteries is often overlooked. Here, we designed a functional separator that not only had a high thermal conductivity of 0.65 W m−1 K−1 but also alleviated the diffusion of dissolved active materials to the lithium anode, improving the electrochemical performance and safety issue. Lithium-sulfur batteries with the functional separator have a specific capacity of 1,126.4 mAh g−1 at 0.2 C, and the specific capacity can be remained up to 893.5 mAh g−1 after 100 cycles. Pouch Cells with high sulfur loading also showed a good electrochemical performance under a lean electrolyte condition of electrolyte/sulfur (E/S) = 3 μL mg−1.

Nano-Ceramic Cathodes via Co-sputtering of Gd–Ce Alloy and Lanthanum Strontium Cobaltite for Low-Temperature Thin-Film Solid Oxide Fuel Cells

We report the electrochemical performance and structural characteristics of porous nanostructured ceramic cathodes for thin-film solid oxide fuel cells (TF-SOFCs) based on yttria-stabilized zirconi...

Fast operando X-ray pair distribution function using the DRIX electrochemical cell.

In situ electrochemical cycling combined with total scattering measurements can provide valuable structural information on crystalline, semi-crystalline and amorphous phases present during (dis)charging of batteries. In situ measurements are particularly challenging for total scattering experiments due to the requirement for low, constant and reproducible backgrounds. Poor cell design can introduce artefacts into the total scattering data or cause inhomogeneous electrochemical cycling, leading to poor data quality or misleading results. This work presents a new cell design optimized to provide good electrochemical performance while performing bulk multi-scale characterizations based on total scattering and pair distribution function methods, and with potential for techniques such as X-ray Raman spectroscopy. As an example, the structural changes of a nanostructured high-capacity cathode with a disordered rock-salt structure and composition Li4Mn2O5 are demonstrated. The results show that there is no contribution to the recorded signal from other cell components, and a very low and consistent contribution from the cell background.

Nanostructured BaCo0.4Fe0.4Zr0.1Y0.1O3-δ Cathodes with Different Microstructural Architectures.

Lowering the operating temperature of solid oxide fuel cells (SOFCs) is crucial to make this technology commercially viable. In this context, the electrode efficiency at low temperatures could be greatly enhanced by microstructural design at the nanoscale. This work describes alternative microstructural approaches to improve the electrochemical efficiency of the BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) cathode. Different electrodes architectures are prepared in a single step by a cost-effective and scalable spray-pyrolysis deposition method. The microstructure and electrochemical efficiency are compared with those fabricated from ceramic powders and screen-printing technique. A complete structural, morphological and electrochemical characterization of the electrodes is carried out. Reduced values of area specific resistance are achieved for the nanostructured cathodes, i.e., 0.067 Ω·cm2 at 600 °C, compared to 0.520 Ω·cm2 for the same cathode obtained by screen-printing. An anode supported cell with nanostructured BCFZY cathode generates a peak power density of 1 W·cm−2 at 600 °C.

A High-Rate Lithium Manganese Oxide-Hydrogen Battery.

Rechargeable hydrogen gas batteries show promises for the integration of renewable yet intermittent solar and wind electricity into the grid energy storage. Here, we describe a rechargeable, high-rate, and long-life hydrogen gas battery that exploits a nanostructured lithium manganese oxide cathode and a hydrogen gas anode in an aqueous electrolyte. The proposed lithium manganese oxide-hydrogen battery shows a discharge potential of ∼1.3 V, a remarkable rate of 50 C with Coulombic efficiency of ∼99.8%, and a robust cycle life. A systematic electrochemical study demonstrates the significance of the electrocatalytic hydrogen gas anode and reveals the charge storage mechanism of the lithium manganese oxide-hydrogen battery. This work provides opportunities for the development of new rechargeable hydrogen batteries for the future grid-scale energy storage.

Size effects in nanostructured Li-ion battery cathode particles

Abstract Cathode materials for Li-ion batteries exhibit volume expansions on the order of 10% upon maximum lithium insertion. As a result internal stresses are produced and after continuous electrochemical cycling damage accumulates, which contributes to their failure. Battery developers resort to using smaller particle sizes in order to limit damage and some models have been developed to capture the effect of particle size on damage. In this paper, we present a gradient elasticity framework,which couples the mechanical equilibrium equations with Li-ion diffusion and allows the Young’s modulus to be a function of Li-ion concentration. As the constitutive equation involves higher order gradient terms, the conventional finite element method is not suitable, while, the two-way coupling necessitates the need for higher order shape functions. In this study, we employ B-spline functions with the framework of the iso-geometric analysis for the spatial discretization. The effect of the internal characteristic length on the concentration evolution and the hydrostatic stresses is studied. It is observed that the stress amplitude is significantly affected by the internal length, however, using either a constant Young’s modulus or a concentration dependent one yields similar results.