Battery Electrodes Research Articles

Rational synthesis of vertical graphene supported TiN@N-Li4Ti5O12 as advanced high-rate electrodes for lithium-ion batteries

The Li4Ti5O12 (LTO) is demonstrated to be one of the most promising anode materials for lithium-ion batteries (LIBs) to provide safe and high-power density cells but suffer from poor electrical conductivity. In this study, we present a TiN-decorated N-LTO on a vertical graphene (VG) array (TiN@N-LTO) as a potential anode material for lithium-ion batteries (LIBs). The use of atomic layer deposition (ALD) enables the formation of a thin layer of LTO on VG, with precise control over the thickness. The VG serves as highly conductive channels, facilitating the transfer of electrons. Moreover, the introduction of nitrogen heteroatoms into the LTO under an active N2 plasma atmosphere has been shown to enhance its intrinsic conductivity, which is achieved by reducing the bandgap and expanding the diffusion pathways of ions. Concurrently, a small number of metallic TiN are formed and deposited on the surface of N-LTO, thereby further improving its conductivity. COMSOL simulations and DFT calculations demonstrate that the introduced TiN acts as a "conductive bridge", improving the charge distribution of LTO electrodes and enhancing the Li+ transport rate. The TiN@N-LTO exhibits a high rate performance (169.51, 131.61 and 101.08 mAh/g at 0.2, 2 and 20 C, respectively) and remarkable cycling stability (a capacity retention of 99.6% after 5000 cycles at 10 C).

Molecular dynamics study of mechanical stability of Ti4C3 MXene subjected to chirality, temperature, strain rate, and point-vacancy for Lithium-ion batteries

Two-dimensional Ti4C3 MXene has recently emerged as a promising electrode for Lithium-ion batteries (LIBs) because of its outstanding ion-transport abilities and high Li-absorbability. This study employed molecular dynamics simulation to explore the mechanical stability of Ti4C3 MXene subjected to various temperatures, strain rates, and vacancy concentrations. A slightly superior tensile strength and elasticity modulus have been observed along zigzag directions, measuring 148.14 GPa and 29.17 GPa, respectively. On the other hand, armchair-oriented Ti4C3 MXene shows a considerably greater fracture strain of 0.259 due to its strain-hardening tendency at lower temperatures. Elevated temperature decreases both fracture strength and fracture strain, which is opposite to the effect of strain rate. Armchair loading has been revealed to be more sensitive to strain rate than its counter direction. Unlike temperature and strain rate, point vacancy significantly deteriorates the elastic modulus of Ti4C3 MXene. Carbon vacancies are more probable than titanium vacancies, which have less formation energy. The atomistic deformation profile supports the predicted values of fracture strain from stress-strain behavior. This in-depth study offers a detailed understanding of the mechanical behavior of Ti4C3 MXene under diverse circumstances, which will aid further experimental study and be beneficial for adopting Ti4C3 as anode materials in LIBs.

Thermoelectric properties of superionic Li0.11Cu1.89S compound

Copper sulfide is a multifunctional material. Copper sulfides are known to be used in photo-electric converters, in plasmonics, in active electrodes of batteries and supercapacitors, etc. The excellent thermoelectric properties of copper sulfide are well-known too. The purpose of this study is to investigate the thermoelectric performance of nanocomposite copper sulfide contained monoclinic Cu2S and tetragonal Cu1.96S phase. According to scanning electron microscopy, the average particle size of the synthesized powder was about 373 nm. The Li0.11Cu1.89S sample showed an electronic conductivity of 50–180 S/cm, a Seebeck coefficient of 0.04–0.31 mV/K in the range of 300–700 K, and high power factor 5.8 μW K−2cm−1 at 672 K. Total thermal conductivity decreases with increasing temperature from 0.61 to 0.22 W∙K−1m−1 in the range of 300–700 K. Such low thermal conductivity and high power factor made it possible to achieve an extremely high dimensionless thermoelectric figure of merit ZT = 1.76 at 672 K, which allows to consider the Li0.11Cu1.89S alloy as a promising thermoelectric material.

Influence of Conductive Additives and Binder on the Impedance of Lithium-Ion Battery Electrodes: Effect of an Inhomogeneous Distribution

The conductive additive and binder domain (CBD) is an essential component of lithium-ion battery electrodes. It enhances the electrical connectivity and mechanical stability within the solid electrode matrix. Migration of the binder during electrode drying can lead to an inhomogeneous distribution of the CBD, impeding transport of lithium ions into the electrodes, and diminishing the electronic pathways between solid particles and the current collector. This is especially prominent in thick electrodes at high drying rates. Therefore, we investigate the effect of a non-uniform CBD distribution on the electrochemical performance of NMC622 electrodes via microstructure-resolved three-dimensional (3D) simulations on virtual electrodes, based on tomographic image data, and compare them with experimental results. The valuable information derived by combining microstructure-resolved models with electrochemical impedance spectroscopy measurements on symmetric cells under blocking electrolyte conditions is used to characterize the lithium-ion transport in the electrode pore space, including the contributions of the CBD. The effect of this inhomogeneity on electrode performance is then gauged via galvanostatic discharge simulations under changing discharge currents and for varying electrode densities. Through our work, we demonstrate the significance of the CBD distribution and enable predictive simulations for future battery design.

Ultrafast Spectroscopy at the Central Laser Facility

In this article, we will examine ultrafast spectroscopy techniques and applications, covering time-resolved infrared (TR-IR) spectroscopy, time resolved visible (TA) spectroscopy, two-dimensional infrared (2D-IR) spectroscopy, Kerr-gated Raman spectroscopy, time-resolved Raman and surface sum-frequency generation (SSFG) spectroscopy. In addition to introducing each technique, we will cover some basics, such as what kinds of lasers are used and discuss how these techniques are applied to study a diversity of chemical problems such as photocatalysis, photochemistry, electrocatalysis, battery electrode characterisation, zeolite characterisation and protein structural dynamics.

On the Volume Expansion of Lithium Ion Battery Electrodes (I) after Wetting, and (II) Selection of the Right Amount of Electrolyte

The electrolyte is necessary for transport of lithium ions between the negative and positive electrode within the battery cell. The lower the amount of electrolyte, the higher the energy density and specific energy. Hence, it is important to understand which cell parameters are relevant to determine the right amount of electrolyte. Here, three different cell designs in 1 to 5 Ah pouch cells where investigated for cell impedance after filling, cell capacity after formation, C-rate performance, and capacity retention for up to 3,000 full cycles. Wetting the cell with electrolyte, the cell pore volume changed between 25%–35% due to changes of 6%–16% in the thickness of the anode and cathode. Although electrolyte volumes >0.85 times the wet cell pore volume showed minimal resistance before formation, only electrolyte volumes of 1.08 times the wet cell pore volume were sufficient for a successful formation process. For long-term cycling, a minimum electrolyte volume of 1.19 times the wet cell pore volume was required to improve long-term cycling performance. Future experiments will investigate the correlation of capacity fade with electrolyte consumption for different electrolytes.

Visualizing and Quantifying Electronic Accessibility in Composite Battery Electrodes using Electrochemical Fluorescent Microscopy

Electronic connections between active material particles and the conductive carbon binder domain govern high-energy commercial Li-ion batteries' rate capability and lifetime (LIB). This work develops an in situ electrochemical fluorescent microscopy (EFM) technique that maps fluorescence intensity to these local electronic connections. Specifically, rapid redox kinetics of an electrofluorophore translates to reaction distributions limited by the electronic accessibility of battery electrode regions and individual active material particles. This technique can visualize hot spots, dead zones, and isolated particles on the electrode surface. EFM characterization of a series of LiNi0.33Mn0.33Co0.33O2 electrodes across processing parameters finds a significant negative correlation between the number of disconnected active particles and the rate capability. This low-cost technique provides quantitative mesoscale characterization of commercial LIB electrodes with fast throughput (<60 s) to facilitate rapid research and development and provide manufacturing quality control.

3D-Printed Carbon Scaffold for Structural Lithium Metal Batteries.

Focus on advancement of energy storage has now turned to curbing carbon emissions in the transportation sector by adopting electric vehicles (EVs). Technological advancements in lithium-ion batteries (LIBs), valued for their lightweight and high capacity, are critical to making this switch a reality. Integrating structurally enhanced LIBs directly into vehicular design tackles two EV limitations: vehicle range and weight. In this study, 3D-carbon (3D-C) lattices, prepared with an inexpensive stereolithography-type 3D printer followed by carbonization, are proposed as scaffolds for Li metal anodes for structural LIBs. Mechanical stability tests revealed that the 3D-C lattice can withstand a maximum stress of 5.15 ± 0.15MPa, which makes 3D-C lattices an ideal candidate for structural battery electrodes. Symmetric cell tests show the superior cycling stability of 3D-C scaffolds compared to conventional bare Cu foil current collectors. When 3D-C scaffolds are used, a small overpotential (≈0.075V) is retained over 100 cycles at 1mA cm-2 for 3 mAh cm-2, while the overpotential of a bare Cu symmetric cell is unstable and increased to 0.74V at the 96th cycle. The precisely oriented internal pores of the 3D-C lattice confine lithium metal deposits within the 3D scaffold, effectively preventing short circuits.

Fabrication of cerium vanadate-embedded on carbon based graphene material (rGO) with significant performance for supercapacitor electrode

This work examined the electrochemical properties of CeVO3 nanocomposite that were enhanced with reduced graphene oxide (rGO) and CeVO3 nanoparticles. The CeVO3/rGO fabricated using a typical hydrothermal process that was further characterized via XRD revealed the monoclinic crystalline structure of the CeVO3 nanoparticles. The presence of uniformly distributed particles structured CeVO3 and layer-structured (rGO) reduced graphene oxide in the nanocomposite materials was determined using scanning electron microscopy pictures. We evaluated the electro-chemical efficiency of the nanocrystals for enhanced working electrodes and supercapacitors with cerium vanadate (CeVO3) nanoparticles and the cerium vanadate (CeVO3) embedded on reduced graphene oxide (rGO). The analysis was conducted on 2.0 M aqueous KOH (potassium hydroxide) electrolytic solution and it achieved the capacitance of 355.46 F g−1 (10 mVs−1) was concluded by cyclic voltammetry analysis of the working electrode modified with pure CeVO3 nanomaterial. The addition of rGO improved the value of Cs to 947.30 F g−1 at the same scan speed (10 mVs−1). The CeVO3 nanoparticles and CeVO3/rGO nanocomposite exhibited the capacitance values of 698.54 F g−1 and 1403.35 F g−1 at 1 A g−1 respectively, as determined by GCD analysis. The fabricated with CeVO3 nanoparticles exhibited power density values of 254.1 W kg−1 and energy values of 25.05 W h kg−1. On the other hand, the CeVO3/rGO nanocomposite showed greater energy (Ed) and power (Pd) density of 54.72 W h kg−1 and 264.95 W kg−1, individually. After undergoing 5000th cycles, the material utilizing CeVO3/rGO composite maintained its stability. The electrochemical examination of the synthesized cerium vanadate nanoparticles revealed that the inclusion of rGO resulted in a hybrid capacitive nature and the proposed nanocomposite can be employed as supercapacitors or as electrodes in batteries as well as energy storage and generating device for future use.

Influence of 3D Structural Design on the Electrochemical Performance of Aluminum Metal as Negative Electrode for Li-Ion Batteries.

Aluminum (Al) is one of the most promising active materials for producing next-generation negative electrodes for lithium (Li)-ion batteries. It features low density, high specific capacity, and low working potential, making it ideal for producing energy-dense cells. However, this material loses its electrochemical activity within 100 cycles, making it practically unusable. Several claims in the literature support the idea that a dual degradation mechanism is at play. First, the slow diffusion of Li in the Al matrix causes the electrochemical reactions to be partly irreversible, making the initial capacity of the cell drop. Second, the stress caused by cycling make the active material pulverize and lose activity. Recent work shows that shortening the diffusion path of Li by 3D structuring is an effective way to mitigate the first capacity loss mechanism, while alloying Al with other elements effectively mitigates the second one. In this work, we demonstrate that the benefits of 3D structuring and alloying are cumulative and that a mesh made of an Al-magnesium alloy performs better than both a pure Al foil and a foil of an Al-Mg alloy.

Carbon-Binder-Domain porosity extraction through lithium-ion battery electrode impedance data

In the field of 3-D resolved computational modelling of Lithium-ion battery electrodes, the arrangement and properties of the Carbon-Binder-Domain (CBD) play a critical role in the ion and electron transport properties through their impact on the electrode tortuosity factor. However, until now, the CBD porosity value -its main descriptor in terms of transport properties and occupied volume- has been determined through educated guesses due to the lack of an experimental approach. Here, a novel methodology is reported for the determination of the CBD internal porosity through the combination of computational modelling and experimental electrochemical impedance spectroscopy (EIS). The methodology is based on the creation of a calibration curve that relates tortuosity factor with CBD porosity through digital stochastic generation of electrode microstructures and diffusivity characterization. The curve is then compared to the EIS experimental results and analyzed through a transmission line model, yielding a good estimation of the parameters. In this work, the usefulness and the identified limitation of this approach are demonstrated using three different formulations of LiNi0.3Mn0.3Co0.3O2 (NMC 111) cathodes. To the best of the authors’ knowledge, this is the first reported method for estimating CBD porosity.

Machine learning-based design of electrocatalytic materials towards high-energy lithium||sulfur batteries development

The practical development of Li | |S batteries is hindered by the slow kinetics of polysulfides conversion reactions during cycling. To circumvent this limitation, researchers suggested the use of transition metal-based electrocatalytic materials in the sulfur-based positive electrode. However, the atomic-level interactions among multiple electrocatalytic sites are not fully understood. Here, to improve the understanding of electrocatalytic sites, we propose a multi-view machine-learned framework to evaluate electrocatalyst features using limited datasets and intrinsic factors, such as corrected d orbital properties. Via physicochemical characterizations and theoretical calculations, we demonstrate that orbital coupling among sites induces shifts in band centers and alterations in the spin state, thus influencing interactions with polysulfides and resulting in diverse Li-S bond breaking and lithium migration barriers. Using a carbon-coated Fe/Co electrocatalyst (synthesized using recycled Li-ion battery electrodes as raw materials) at the positive electrode of a Li | |S pouch cell with high sulfur loading and lean electrolyte conditions, we report an initial specific energy of 436 Wh kg−1 (whole mass of the cell) at 67 mA and 25 °C.

Flotation separation of lithium–ion battery electrodes predicted by a long short-term memory network using data from physicochemical kinetic simulations and experiments

Anode and cathode active materials from spent lithium–ion batteries may be recovered and potentially used in new batteries to promote recycling and resource circulation. Froth flotation was applied to pristine active materials and the black mass obtained from pretreated spent batteries. Flotation kinetics was simulated with the use of computational fluid dynamics and surface chemistry. Bubble surface coverage and entrainment in the flotation kinetics model were selected and optimized by systematic fitting to experimental data. Entrainment influences the recovery and grade of the active materials. The optimized flotation kinetics model was used for generating additional data that, along with the fitted data, were used to train a deep learning neural network. The trained network was validated using anode–cathode and black mass flotation experiments, and its predictions showed a maximum residual error of 0.18 ± 0.11 recovery. The simulation framework was developed into a desktop application that predicts the flotation behavior of active materials. It provides information for estimating results following operational and physicochemical changes and for optimizing flotation processes. Finally, recovered anode active materials from black mass were selected for coin cell tests. The coulombic efficiency of these coin cells was initially lower (86.8 %) than that of cells made with pristine graphite particles (98.4 %).

Modeling and analysis of solvent removal during lithium-ion battery electrode drying: A semi-conjugate approach

The solvent removal process is one of the most energy intensive step in the production of lithium-ion batteries. However, the process is not well understood due to the different driving forces of the solvent liquid transport involved. Here, a semi-conjugate model that considers the effects of jet impingement on the electrode drying process is developed to investigate the solvent removal mechanism. Three different drying stages are observed. The driving force in the heating stage is due to the increase in electrode temperature. Heat transfer between the electrode and jet impingement dominates the drying process during the constant rate stage. Mass transfer in the porous electrode is the main factor affecting the drying process during the falling rate stage. Finally, the effects of process parameters such as jet temperature on the drying process are discussed. A three-stage drying process is proposed to reduce energy consumption while maintaining drying efficiency.

A general methodology for the in situ construction of MxSy@N,S-C composites from L-cysteine for sodium-ion battery applications

High-capacity metal sulfides have been extensively investigated as cathode materials for secondary batteries. Despite their high capacity, the redox potential of metal sulfides is limited to 2.7 V. Therefore, researchers explored its application as a negative electrode material and discovered its exceptional electrochemical performance. However, the conventional methods for synthesizing transition metal sulfides (TMS) inevitably require an external source of sulfur for secondary sulfidation, resulting in energy dissipation. In this study, L-cystine was adopted as a polydentate ligand for the synthesis of MxSy@N, SC metal-organic frameworks, which can confine the desired carbon, nitrogen, and sulfur sources within the framework. This approach facilitates one-step sintering to obtain nitrogen-doped transition metal sulfides. The structure composition and electrochemical reaction mechanism of FeS@N,S-C as the negative electrode in Na-ion batteries were studied through scanning electron microscopy (SEM)/transmission electron microscopy (TEM) and X-ray diffraction (XRD)/X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical properties of FeS@N,S-C materials were test as an example. The FeS@N, SC composite exhibited a reversible Na+ storage capacity of 724.4 mAh g−1 at a current density of 200 mA g−1, and still maintained a reversible capacity of 600.7 mAh g−1 at a current density of 2000 mA g−1, demonstrating excellent rate performance. After 200 cycles, the material was still able to retain 97.3 % of the discharge specific capacity, demonstrating fine cycle performance. It shows that the FeS@N, SC composite has rapid electron conduction ability and high sodium ion diffusion coefficient. At the same time, a rapidly charge-discharge process can be achieved with a large capacitive contribution, indicating the great potential of this material as a sodium-ion battery.

Solution combustion growth of porous ZnMn2O4 on carbon cloth to enhance zinc ions storage performance

As a positive electrode material for zinc ions storage, the large-scale application of ZnMn2O4 is severely impeded by its low conductivity and inferior cyclic durability. In this study, porous ZnMn2O4 was successfully grown on carbon cloth (ZnMn2O4@CC) for the first time using a solution combustion strategy. In the proposed combustion system, zinc nitrate and manganous nitrate were used as the oxidizing agents, while glucose served as the fuel. The in-situ growth of porous ZnMn2O4 on carbon fiber resulted in a binder-free electrode, with a coaxial core-shell architecture, improving both the structure stability and the electrode's conductivity. Compared to ZnMn2O4 powder, the zinc ions storage performance of ZnMn2O4@CC was significantly enhanced. The ZnMn2O4@CC delivered a 1st discharge-specific capacity of 281.7 mAh g−1 at 100 mA g−1, with 112.2 mAh g−1 of capacity at 500 mA g−1 after 300 cycles. The fabricated ZnMn2O4, with a large specific surface and plentiful mesopores, facilitated the wetting and penetration of the electrolyte. In addition, the porous feature can buffer the stress during the charging and discharging processes, enhancing specific capacity and cycle ability. This work not only introduces a novel method for preparing binder-free electrodes but also explores the potential application of such electrodes in zinc-ion batteries.

Effects of ion mass transport on electrochemical reaction pathways in aluminum-anthraquinone batteries

Aluminum anodes and quinone-based organic cathodes couple as earth abundant, sustainable, and safe battery electrodes. However, different numbers of galvanostatic discharge plateaus have been observed in aluminum-quinone cells depending on the experimental conditions, a phenomenon that has not yet been explained and furthermore affects cell energy density. Here, in aluminum-anthraquinone batteries, we show that ion mass transport affects the electrochemical reaction pathway and controls the occurrence of either one or two reduction plateaus during galvanostatic discharge. The effects of electrode mass loading, porosity, rest periods, and cycling rates were analyzed on the reduction potential and relative specific capacity of the galvanostatic plateaus. When AlCl2+ cations charge compensate the electrochemically reduced carbonyl groups concurrently, a single reduction plateau is observed. When ion mass transport is limiting, sequential reduction and charge compensation of each carbonyl group results in two distinct reduction plateaus. The second plateau occurs at a potential approximately 0.3 V lower than the first, thus decreasing the cell energy density. The potential of the electrochemical oxidation reaction where AlCl2+ cations dissociate, however, is not affected. Ion mass transport is thus shown to be a critical variable that can control the electrochemical reaction pathway, redox potentials, and practical energy densities of aluminum-quinone batteries.

Gas adsorption analysis for quantifying the edge sites of graphite

The edge plane exposed on the surface of carbon materials is the active site that determines their properties. When graphite is used as the negative electrode in lithium-ion batteries, the edge plane acts as an access point for lithium insertion/desorption. However, because of the low specific surface area and amorphous carbon coating of graphite particles, accurately estimating the number of edge planes is challenging. Therefore, we propose a technique for determining graphite edge planes based on the stepwise adsorption of Kr onto the hexagonal carbon network surface. Graphite particles with highly modified surface structures were prepared by controlling the particle size, heat treatment temperature, and amorphous carbon coating. Electrochemical evaluation revealed significant differences in charge-transfer resistance, an indicator of edge planes. The edge plane determination results obtained using conventional methods such as X-ray diffractometry and Raman spectroscopy did not correlate well with charge-transfer resistance. Meanwhile, Kr adsorption measurements revealed that the stepwise adsorption behavior, because of the interaction of Kr with the energetically homogenous surface, varied significantly depending on the surface properties of graphite particles. The number of edge planes estimated by gas adsorption strongly correlated with charge-transfer resistance. Consequently, we determined that the graphite edge plane tied to the electrochemical index can be derived using gas adsorption analysis. This edge plane determination technique would be applicable not only to graphite but also to highly crystalline carbon materials with an exposed hexagonal carbon network surface.

Nitrogen and phosphorus co-doped hard carbon materials as high-performance anode for sodium ion batteries

Abstract The negative electrode of sodium ion batteries has always faced severe challenges in the commercialization process. To improve capacity, increase the first Coulomb efficiency, and enhance performance under high current density, we have prepared a nitrogen phosphorus co-doped hard carbon material. Phosphorus groups are doped in the material to achieve sodium storage, at the same time, coating phenolic resin for material modification. At the same time, nitrogen and carbon nanotube structures are added during the preparation process to make it have good conductivity. In order to solve the problem of low first Coulomb efficiency, adopted CMC binder and ether based electrolyte to solve the problem of excessive reaction between the negative electrode and the electrolyte during the first discharge process. In actual testing, this material has a capacity of 365 mAh g−1 and a capacity retention rate of 112% under long cycles.

Electrolyte Additive l-Lysine Stabilizes the Zinc Electrode in Aqueous Zinc Batteries for Long Cycling Performance.

Rechargeable aqueous Zn-ion batteries (AZIBs) have been recognized as competitive devices for large-scale energy storage due to their characteristics of low cost, safe operation, and environmental friendliness. Nevertheless, their practical applications are greatly limited by zinc dendrite growth and side reactions occurring at the anode/electrolyte interface. Herein, we propose an effective and simple electrolyte engineering strategy, which is the introduction of l-lysine additive containing two amino groups and one carboxyl group into a ZnSO4 electrolyte to achieve stable and reversible Zn depositions. Theoretical calculations and experimental results reveal that the l-lysine can adsorb on the Zn anode surface due to the strong coordination effects between amino groups and Zn metal (Zn-N binding) and induce the reduction of ZnSO4 into inorganic ZnS, which can not only prevent interfacial side reactions but also regulate interfacial electric field on the zinc electrode surface to guide uniform Zn2+ electrodeposition to inhibit zinc dendrites. Consequently, the l-lysine additive in the electrolyte enables Zn||Zn symmetric cells to achieve an ultralong stable cycling up to 2400 h at 1 mA cm-2 with a low polarization of only about 16 mV and Zn||Cu asymmetric cells to obtain a high average Coulombic efficiency of 99.80% after stably cycling for more than 2000 h at 2 mA cm-2 (1 mAh cm-2). In addition, the Zn||MnO2@CNT full cell in an l-lysine-containing electrolyte also exhibits good cycling performance. This study offers a new perspective on multifunctional electrolyte additive for achieving highly reversible Zn metal anodes in AZIBs.