Cathode Surface Research Articles

Enhancing the Structural Stability and Electrochemical Performance of High-Nickel Cathode Materials through Ti Doping with an Exothermic Non-oxide Precursor.

The foreseeable global cobalt (Co) crisis has driven the demand for cathode materials with less Co dependence, where high-nickel layered oxides are a promising solution due to their high energy density and low cost. However, these materials suffer from poor cycling stability and rapid voltage decay due to lattice displacement and nanostrain accumulation. Here, we introduced an exothermic TiN dopant via a scalable coating method to stabilize LiNi0.917Co0.056Mn0.026O2 (NCM92) materials. The exothermic reaction of TiN conversion generates extra heat during the calcination process on the cathode surface, promotes the lithiation process, and tunes the morphology of the cathode material, resulting in compact and conformal smaller particle sizes to provide better particle integration and lithium diffusion coefficient. Moreover, the Ti dopant substitutes the Ni3+ site to generate stronger Ti-O bonding, leading to higher structural stability and extended cycle life. The Ti-doped NCM (NCM92_TiN) shows a remarkable cycling stability of maintaining 80% capacity retention for 400 cycles, while bare NCM92 can only reach 88 cycles. Furthermore, the NCM92_TiN cathodes demonstrate an enhanced rate capability and achieve a discharge capacity of over 168 mAh g-1 at 5C.

Solid polymer electrolytes regulated by ion-dipole interactions for high voltage lithium batteries

Solid polymer electrolytes (SPEs) with wide electrochemically stable window and high lithium-ion transference number (tLi+) are a requirement for high energy density lithium batteries. Here, we construct a copolymer electrolyte (PDA) with ether-ester bifunctional groups that exhibits a low highest occupied molecular orbital (HOMO) energy level by in situ polymerization. Compared to the poly(1,3-dioxolane) (PDOL) pure polyether electrolyte, the weakening of the ion-dipole interaction between lithium salt and polymer in the PDA electrolyte promotes the formation of a “weak solvation” structure. Therefore, the electrolyte achieves high oxidative stability (4.6 V vs. Li+/ Li with a standard leakage current of 10 μA), high Li+ transference number (0.60), and importantly, derives a stable LiF-rich composition on high voltage cathode surface. Which ultimately enables stable cycling of Li||LiNi0.5Co0.2Mn0.3O2 (NCM523) batteries at a range of 3.0–4.3 V. This work provides a fundamental understanding of the design of antioxidant SPEs to achieve high energy density lithium batteries.

Enhancing the Cathode/Electrolyte interface in Ni-Rich Lithium-Ion batteries through homogeneous oxynitridation enabled by NO3− dominated clusters

To meet the demand for higher energy density in lithium-ion batteries, extensive research has focused on advanced cathodes and metallic lithium anodes. However, Ni-rich cathodes suffer from the inactive phase-transition and side reactions at the cathode-electrolyte interfaces (CEI). In this study, we propose a novel approach to enhance the solubility of LiNO3 in carbonate electrolyte systems using a local high-concentrated addition strategy with triethyl phosphate as a co-solvent. Rather than the traditional solvent-dominated solvation clusters, the NO3− dominated electrolyte is examined to elucidate unique complexation phenomena. Two distinct clusters in NO3− dominated electrolyte arising from as a consequence of intramolecular interactions intrinsic to the constituents. This promotes the formation of a homogeneous oxynitride interphase and facilitates more expeditious lithium ion diffusion kinetics. Hence, the less stress fragmentation and irreversible phase transformation occur on the cathode surface with the homogeneous oxynitridation interface. This innovative design enables efficient cycling of the Li || NCM811 cell, offering a promising strategy to improve lithium-ion batteries performance.

In Situ Electrochemical Polymerization of Cathode Electrolyte Interphase Enabling High-Performance Lithium Metal Batteries.

Lithium metal batteries (LMBs) with high-voltage nickel-rich cathodes show great potential as energy storage devices due to their exceptional capacity and power density. However, the detrimental parasitic side reactions at the cathode electrolyte interface result in rapid capacity decay. Herein, a polymerizable electrolyte additive, pyrrole-1-propionic acid (PA), which can be in situ electrochemically polymerized on the cathode surface and involved in forming cathode electrolyte interphase (CEI) film during cycling is proposed. The formed CEI film prevents the formation of microcracks in LiNi0.8Co0.1Mn0.1O2 (NCM811) secondary particles and mitigates parasitic reactions. Additionally, the COO- anions of PA promote the acceleration of Li+ transport from cathode particles and increase charging rates. The Li||NCM811 batteries with PA in the electrolyte exhibit a high capacity retention of 83.83% after 200 cycles at 4.3V, and maintain 80.88% capacity after 150 cycles at 4.6V. This work provides an effective strategy for enhancing interface stability of high-voltage nickel-rich cathodes by forming stable CEI film.

Practical surface-reconstruction strategy based on self-reactive interface design enables ultralong cyclability of commercial cathodes for lithium-ion batteries

Although Al-doped high-voltage LiCoO2 (HVLCO) cathode has been widely used in commercial lithium-ion batteries, it still suffers from poor cycling stability due to its unstable surface/interface structure causing bad side reactions. Herein, a surface reconstruction strategy based on self-reactive interface design has been proposed, to construct a uniform and ultrathin (∼ 5 nm) LiAlO2 (LAO) layer on the surface of HVLCO cathodes. The construction of LAO layer is realized by a facile and scalable process involving chemical immersion in LiOH solution and subsequent heating treatment. Moreover, the LAO coating layer imparts both lower interior stress upon lithiation and lower migration energy barrier of Li ions, guaranteeing stable and rapid lithium storage, which is confirmed by substantial characterizations and theory calculations. Consequently, ultralong cycle life over 10,000 h (1000 cycles) at 0.1 C is achieved for the surface-reconstructed HVLCO cathode, with an 86% capacity retention. Especially, different kinds of commercial HVLCO products as well as NCM (LiNi0.6Co0.2Mn0.2O2) cathode material, after the same surface reconstruction, also show remarkably reinforced electrochemical performance. This practical surface-reconstruction strategy may serve as a useful guideline for future design and performance optimization of commercial cathode materials.

Electrochemical instability of room-temperature ionic liquids with LiTFSI at elevated temperature and its consequences in Li/Li-ion based half-cells and full-cells

High-temperature Li-ion batteries capable of operating up to 100 ℃ can replace lithium thionyl chloride primary batteries in specialized industrial applications. Room-temperature ionic liquids (RTIL) offer high thermal stability and can be a promising choice of electrolyte for high-temperature batteries. This work elucidates that high thermal stability alone does not guarantee effective battery operation due to the electrochemical instability observed in RTIL-LiTFSI mixtures at elevated temperatures. Here, we investigate the impact of varying electrochemical stability in RTILs on half-cell, full-cell, and calendar aging. Electrochemical instability of the electrolyte at the cathode interface injects additional electrons and Li-ions into the electrochemical cell, triggering a cascade of detrimental chain reactions that hinder efficient battery performance. We demonstrate that electrochemical information gathered from a full-cell configuration can frequently obscure the presence of electrochemical instability at the cathode surface. To accurately evaluate this instability, it is essential to perform in-depth half-cell studies and other characterizations. Our results indicate that cathode electrolyte interphase (CEI) can reach a thickness of up to 100 nm, with a depth-dependent composition showing higher concentration of inorganic species like LiF and LiNSO near the cathode surface. Further, accelerated calendar aging measurements of such cells at high temperature revealed complete irreversible self-discharge within as little as 14 days. These findings shed light on the critical factors influencing the stability and performance of cells under challenging operating conditions.

Ionic Liquids as Cathode Additives for High Voltage Lithium Batteries

AbstractTwo oxalatoborate ionic liquids (ILs), which are commonly utilized as electrolyte additives that form a protective layer on the cathode surface, are investigated for the first time as electrode additives. Cathodes based on LiNi0.5Mn1.5O4 (LNMO) containing 3 wt % ILs, i. e., “IL‐enriched cathodes”, exhibit capacity values above 120 mAh/g with high Coulombic efficiencies throughout cycling over 200 times. A cathode without ILs also exhibits a capacity of 119 mAh/g but its Coulombic efficiency becomes low and unstable after 109 cycles. In addition, when 0.3 M ILs are added to conventional carbonate‐based electrolytes, the battery cycle life improves but there is a reduction in the capacity probably due to low ionic conductivity of the electrolyte mixtures. Post‐mortem analyses of electrodes retrieved from cycled cells highlight less electrolyte decomposition and less cathode corrosion, enabled by using the IL as the additive in LNMO, which are confirmed by a particle shape with smooth surface identical to the fresh cathode. The study demonstrates that oxalatoborate ILs can be used as the electrode additive, and this provides a new concept for cathode formulations for high performance batteries with a small amount of ILs.

Study of the effect of spark radius model upon the performance characteristics in EDM process

The evaluation of performance characteristics is of key importance to the EDM process technological reliability. By correctly estimating the power fraction and plasma flushing efficiency, it is possible to improve the accuracy of the surface integrity prediction of the EDM discharge models. In the present research, a combined computational and experimental approach is employed to study the effect of spark radius model upon the performance characteristics in EDM of Ti-6Al-4V alloy. Two famous spark radius relationships have been implemented and the effect on power fraction and removal efficiency was examined for a range of machining conditions. It has been found that the sparking radius relationship accounting for discharge current effect captures the essential dynamics of the EDM process and offers improved prediction accuracy. In such a case, the power fraction going to the cathode ranges from 8.5 to 24 %. When a cooper electrode is utilized, removal efficiency of up to 12 % was observed on the cathode surface. For specific machining conditions, an approximate constant ratio of 2.5 is seen between the power fractions transmitted to the cathode and tool-anode. Crater volume was computed and compared to the experiment to validate the proposed approach. The results of this comparison challenge the EDM model underlying assumption viability, which considers similarity between recast layer and electrode materials thermophysical proprieties when a hydrocarbon-based dielectric fluid is used. From a qualitative perspective, though, the outcomes are still encouraging and indicate that surface integrity in the EDM of Ti-6Al-4V alloy may be predicted using the performance characteristics found in this study.

Contrasting Views of the Electric Double Layer in Electrochemical CO2 Reduction: Continuum Models vs Molecular Dynamics.

In the field of electrochemical CO2 reduction, both continuum models and molecular dynamics (MD) models have been used to understand the electric double layer (EDL). MD often focuses on the region within a few nm of the electrode, while continuum models can span up to the device level (cm). Still, both methods model the EDL, and for a cohesive picture of the CO2 electrolysis system, the two methods should agree in the regions where they overlap length scales. To this end, we make a direct comparison between state-of-the-art continuum models and classical MD simulations under the conditions of CO2 reduction on a Ag electrode. For continuum modeling, this includes the Poisson-Nernst-Planck formulation with steric (finite ion size) effects, and in MD the electrode is modeled with the constant potential method. The comparison yields numerous differences between the two modeling methods. MD shows cations forming two adsorbed layers, including a fully hydrated outer layer and a partial hydration layer closer to the electrode surface. The strength of the inner adsorbed layer increases with cation size (Li+ < Na+ < K+ < Cs+) and with more negative applied potentials. Continuum models that include steric effects predict CO2 to be mostly excluded within 1 nm of the cathode due to tightly packed cations, yet we find little evidence to support these predictions from the MD results. In fact, MD shows that the concentration of CO2 increases within a few Å of the cathode surface due to interactions with the Ag electrode, a factor not included in continuum models. The EDL capacitance is computed from the MD results, showing values in the range of 7-9 μF cm-2, irrespective of the electrolyte concentration, cation identity, or applied potential. The direct comparison between the two modeling methods is meant to show the areas of agreement and disagreement between the two views of the EDL, so as to improve and better align these models.

Li1.4Al0.4Ge0.1Ti1.5(PO4)3: A stable solid electrolyte for Li-CO2 batteries

In this study, a solid electrolyte, Li1.4Al0.4Ge0.1Ti1.5(PO4)3 (LAGTP), with a sodium superionic conductor-type crystal structure, was prepared using a facile solution-based method. LAGTP exhibited exceptional ionic conductivity (1.05 × 10−3 S cm−1) and a low activation energy (0.237 eV). The LAGTP pellet was employed as a solid-state electrolyte in a Li-CO2 battery, showcasing charge-discharge characteristics via a reversible electrochemical reaction (4Li+ + 3CO2 ↔ 2Li2CO3 + C). As-synthesized multi-walled carbon nanotubes, drop-cast on carbon cloth, were used as the cathode. The battery underwent 60 cycles with a cut-off capacity of 1000 mAh g−1 at various current densities, and a full-depth charge and discharge test was conducted at 100 mA g−1. During the charge/discharge process, the particle size of the dead lithium increased on the cathode surface, leading to the blockage of active sites for conversion. Post-cycling analyses were performed to elucidate the cathode degradation mechanism. The incorporation of LAGTP significantly enhanced battery cycle life and safety, making it a suitable candidate for use in next-generation, high-performance Li-CO2 batteries.

Investigation of Pyridine as a Cocatalyst for the CO2 Reduction Reaction on the Cu2O Cathode Surface

Investigation of Pyridine as a Cocatalyst for the CO₂ Reduction Reaction on the Cu₂O Cathode Surface

Cationic Covalent Organic Framework Coating of the Ni-Rich Cathode Surface for the Significant Improvement of the Interfacial Li+ Transport and Structural Stability

Cationic Covalent Organic Framework Coating of the Ni-Rich Cathode Surface for the Significant Improvement of the Interfacial Li⁺ Transport and Structural Stability

VACUUM SYSTEM FOR COATING PARTS OF ROCKET AND SPACE EQUIPMENT

A vertical type vacuum plant was created for applying coatings using the ion-plasma deposition method to the inner surface of hollow products with a diameter of up to 200 mm and a length of up to 1000 mm. The plant includes: a vacuum chamber with a vacuum system, an evaporator with a magnetic system, a power supply and control system, a cooling system. Radial evaporation cathode of tubular shape with controlled arc is used. Inside the cathode is a magnetic system that controls the movement of cathode spots on its surface. Permanent magnets create arched magnetic fields that hold the position of the discharge track in the tangential direction. The trajectory of the movement of the cathode spots has the form of an ellipse stretched along the cathode. For uniform spraying of the cathode surface, the track moves in two directions: around the circumference of the cathode surface and along its length. A mechanism for moving the magnetic system is mounted on the cover of the vacuum chamber. The product to be coated is mounted inside the vacuum chamber in a vertical position thanks to the removable top cover. The necessary rarefaction of the atmosphere (vacuum) is achieved with the help of two vacuum pumps. Coating materials are traditional Сr and Ni-Cr alloys. A feature of the coating structure is presented: the formation of a combination of solid condensed and soft droplet phases. The droplet phase is a part of the evaporator material with several times lower hardness compared to the nitrided condensed phase. The distribution of the soft phase in a strong coating prevents its brittleness, which is important for thick coatings. The disadvantage of the vacuum-arc deposition process is the heating of the part to a temperature of 380-450 °C. To exclude the softening of the main metal of the combustion chamber and nozzle, it is recommended to use bronze alloys with a recrystallization temperature of at least 500 °C.

Perspectives on microbial fuel cells cathode improvement for bioenergy generation

Studies have shown the unlimited benefits attributed to using microbial fuel cell (MFC) in our scientific societies for the conversion of organic waste materials into bio-energy with the aid of micro-organisms catalyzed anode and enzymatic-microbial influenced cathode via electrochemical reactions. However, numerous shortcomings calling for serious investigations have equally been identified despite the inestimable benefits of this clean energy technology. A major one is the need for MFC cathode improvement to enhance bioenergy generation. The current situations and challenges of using MFC together with loop holes that are needed to be filled by researchers were critically explained. Additionally, this paper examines the importance of microbial fuel cells (MFCs) as a source of renewable energy generation. The major focus was on techniques of improving the output of MFCs via its cathode. The addition of catalyst on cathode surface, upscale integration of MFCs and antifouling of gas diffusion electrodes used in MFCs were discussed. Relevant areas that can be considered for future research on improvement of MFCs cathode for long term operation were stated.

Characterization of Co–Ni–TiO2 coatings prepared by combined sol-enhanced and pulse current electrodeposition methods

Abstract This research comprehensively explores the synthesis of Co–Ni–TiO2 coatings employing a hybrid methodology that integrates sol-enhanced and pulse current electrodeposition techniques. The investigation examined the surface morphology and intrinsic properties of Co–Ni–TiO2 coatings, revealing the significant influence of pulse duty cycle variations on the characteristics of coatings. A detailed analysis indicates that a pulse duty cycle of 0.4 optimized the coating’s performance, offering superior attributes compared to other duty cycle settings. The study elucidates that lower duty cycles foster hydrogen evolution reactions on the cathode surface, culminating in the formation of a porous, needle-like coating structure. Conversely, higher duty cycles are found to mitigate the effects of material replenishment, thereby affecting the coating’s quality and performance. The findings of this investigation not only shed light on the critical relationship between the pulse duty cycle and the properties of Co–Ni–TiO2 coatings but also lay a foundational framework for the further refinement and optimization of these coatings for advanced applications.

A Zero-Gap Gas Phase Photoelectrolyzer for CO2 Reduction with Porous Carbon Supported Photocathodes.

A modified Metal-Organic Framework UiO-66-NH2-based photocathode in a zero-gap gas phase photoelectrolyzer was applied for CO2 reduction. Four types of porous carbon fiber layers with different wettability were employed to tailor the local environment of the cathodic surface reactions, optimizing activity and selectivity towards formate, methanol, and ethanol. Results are explained by mass transport through the different type and arrangement of carbon fiber support layers in the photocathodes and the resulting local environment at the UiO-66-NH2 catalyst. The highest energy-to-fuel conversion efficiency of 1.06 % towards hydrocarbons was achieved with the most hydrophobic carbon fiber (H23C2). The results are a step further in understanding how the design and composition of the photoelectrodes in photoelectrochemical electrolyzers can impact the CO2 reduction efficiency and selectivity.

Direct evidence of low work function on SrVO3 cathode using thermionic electron emission microscopy and high-field ultraviolet photoemission spectroscopy

Perovskite SrVO3 has recently been proposed as a novel electron emission cathode material. Density functional theory (DFT) calculations suggest multiple low work function surfaces, and recent experimental efforts have consistently demonstrated effective work functions of ∼2.7 eV for polycrystalline samples, both results suggesting, but not directly confirming, that some fraction of even lower work function surface is present. In this work, thermionic electron emission microscopy (ThEEM) and high-field ultraviolet photoemission spectroscopy (UPS) are used to study the local work function distribution and measure the work function of a partially oriented- (110)-SrVO3 perovskite oxide cathode surface. Our results show direct evidence of low work function patches of about 2.0 eV on the cathode surface, with a corresponding onset of observable thermionic emission at 750 °C. We hypothesize that, in our ThEEM and UPS experiments, the high applied electric field suppresses the patch field effect, enabling the direct measurement of local work functions. This measured work function of 2.0 eV is comparable to the previous DFT-calculated work function values of the SrVO-terminated (110) SrVO3 surface (2.3 eV) and SrO-terminated (100) surface (1.9 eV). The measured 2.0 eV value is also much lower than the work function for the (001) LaB6 single crystal cathode (∼2.7 eV) and comparable to the effective work function of B-type dispenser cathodes (∼2.1 eV). If SrVO3 thermionic emitters can be engineered to access domains of this low 2.0 eV work function, they have the potential to significantly improve thermionic emitter-based technologies.

Constructing a raincoat-like protective layer on sulfur cathode for aqueous Zn–S batteries

The unwanted disproportionation reactions between sulfur and water seriously deteriorate the cycling performance of aqueous Zn−S batteries, but there is not yet effective strategy to address this dilemma. Here, we proposed a concept of putting a “raincoat” on the S cathode to suppress the aforementioned side reactions. Via adding trace amounts of rationally selected organic ligands to the ZnSO4-based electrolyte, a layer of hundreds nanometer thick metal−organic complexes can be in-situ formed on the cathode surface during the charging process. Although the as-formed raincoat-like protecting layer is much thicker than traditional cathode electrolyte interphase (CEI), it has similar functions with CEI, which can not only block the contact between sulfur and aqueous electrolyte, but also effectively transfer Zn2+ during the charging/discharging process. As a result, the obtained aqueous Zn−S batteries delivered a high specific capacity of 1478 mAh g−1 at 0.1 A g−1, and much-improved stability over 300 cycles at 2 A g−1. Moreover, they also delivered an extremely high areal capacity of 4.2 mAh cm−2 and extraordinary cyclic stability even under harsh condition (E/S ratio, 8 μL mg−1, N/P ratio, ∼1.5). We also prove the universality of this strategy to different kinds of S-based cathodes for aqueous Zn−S batteries.

ELECTROCHEMICAL REDUCTION OF ELEMENTAL SULFUR IN ETHYLENE GLYCOL ELECTROLYTE

The work is devoted to the study of the mechanism of reduction of elemental sulfur from ethylene glycol. For this purpose, linear and cyclic voltampere polarization curves were recorded. The influence of sulfur concentration in ethylene glycol electrolyte, potential unfolding rate and temperature on the sulfur reduction process was investigated. By recording the cyclic polarization curve, the range of potentials at which the reduction of elemental sulfur and its anodic oxidation occur was determined. It has been established that an increase in the concentration of sulfur in the electrolyte and temperature raises the speed of its reduction, and the process itself is controlled by the diffusion of sulfur ions to the cathode surface. In addition, the polarization curves on the platinum rotating disc electrode were recorded. The obtained data, namely the rectilinear dependence of ip on the rotation speed of the electrode (ω) to the power of 0.5, confirm the proposal that the process of reduction of elemental sulfur is accompanied by diffusion polarization. The dependence of the current density on the rotation speed of the electrode to the power of 0.5 at different potentials showed that the process of reduction of elemental sulfur in non-aqueous ethylene glycol at potentials of (0.25÷0.4 V) is accompanied by diffusion polarization, whereas at potentials above 0.4 V, it is accompanied by electrochemical polarization. Keywords : Sulfur ions, electroreduction, polarization, scanrate.

Effect of sulfidation on ethaline-assisted electrodeposited iron sulfide-based electrocatalyst for efficient saline water splitting

This study investigated the synthesis of ethaline-assisted iron sulfide on nickel foam (NF) using the electrodeposition method to facilitate saline water splitting. The oxidization of iron and the formation of Fe(OH)3 on the cathode surface pose challenges for the electrodeposition of iron sulfide from aqueous solutions. To tackle these issues, deep eutectic solvent-assisted electrodeposition and ethaline-assisted sulfidation methods have been investigated for synthesizing FeS2. These approaches aim to enhance the efficiency of the iron sulfide electrode by preventing unwanted oxidation and ensuring the formation of high-quality coatings. Sulfidation in non-aqueous media was performed at varying durations, revealing that sulfur content significantly impacts the morphology of the prepared electrode. The optimum FeS2/NF catalyst offers the lowest overpotential of 194 mV at 10 mA cm−2 for oxygen evolution reaction (OER) and 176 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) in saline water splitting. The enhanced catalytic activity is attributed to the formation of multiphasic components in the catalyst. The electrodes exhibited stability in saline water conditions for approximately 10 h for both OER and HER. Moreover, FeS2/NF exhibited stability for 50 h in OER and 20 h in HER when applied to pure water splitting. The investigation explores the unique synthesis of FeS2 in non-aqueous media and examines its catalytic activity in saline water electrolysis.