Electrode-electrolyte Interface Research Articles

Cu-N Synergism Regulation to Enhance Anionic Redox Reversibility and Activity of Li- and Mn-Rich Layered Oxides Cathode.

Anionic redox chemistry enables extraordinary capacity for Li- and Mn-rich layered oxides (LMROs) cathodes. Unfortunately, irreversible surface oxygen evolution evokes the pernicious phase transition, structural deterioration, and severe electrode-electrolyte interface side reaction with element dissolution, resulting in fast capacity and voltage fading of LMROs during cycling and hindering its commercialization. Herein, a redox couple strategy is proposed by utilizing copper phthalocyanine (CuPc) to address the irreversibility of anionic redox. The Cu-N synergistic effect of CuPc could not only inhibit surface oxygen evolution by reducing the peroxide ion O2 2- back to lattice oxygen O2-, but also enhance the reaction activity and reversibility of anionic redox in bulk to achieve a higher capacity and cycling stability. Moreover, the CuPc strategy suppresses the interface side reaction and induces the forming of a uniform and robust LiF-rich cathode electrolyte, interphase (CEI) to significantly eliminate transition metal dissolution. As a result, the CuPc-enhanced LMRO cathode shows superb cycling performance with a capacity retention of 95.0% after 500 long-term cycles. This study sheds light on the great effect of N-based redox couple to regulate anionic redox behavior and promote the development of high energy density and high stability LMROs cathode.

Dynamics and Energetics of Ion Adsorption at the Interface between a Pure Ionic Liquid and Carbon Electrodes.

Molecular dynamics simulations have been used extensively to determine equilibrium properties of the electrode-electrolyte interface in supercapacitors held at various potentials. While such studies are essential to understand and optimize the performance of such energy storage systems, investigation of the dynamics of adsorption during the charge of the supercapacitors is also necessary. Dynamical properties are especially important to get an insight into the power density of supercapacitors, one of their main assets. In this work, we propose a new method to coarse-grain simulations of all-atom systems and compute effective Lennard-Jones and Coulomb parameters, allowing subsequently to analyze the trajectories of adsorbing ions. We focus on pure 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in contact with planar carbon electrodes. We characterize the evolution of the ion orientation and ion-electrode distance during adsorption and show that ions reorientate as they adsorb. We then determine the forces experienced by the adsorbing ions and demonstrate that Coulomb forces are dominant at a long range while van der Waals forces are dominant at a short range. We also show that there is an almost equal contribution from the two forces at an intermediate distance, explaining the peak of ion density close to the electrode surface.

Structural energy storage composites based on etching engineering Fe-doped Co MOF electrode toward high energy density supercapacitors

Metal organic frameworks (MOFs) have been used widely as cathode materials for supercapacitors because of their adjustable chemical composition, variable topological structures, and relatively simple synthesis methods. However, most MOFs are insulated and their metal organic ligand coordination bonds are not stable enough in electrolytes, which greatly limits the application of MOFs in supercapacitors. The synergistic effect between transition metal doped and chemical etching is of great significance for the preparation of high-performance MOF electrodes. This study introduces Fe into Co MOF prepared by co precipitation to optimize the electronic structure of Co, and then constructed e-Fe-doped Co MOF hierarchical structure through ammonia etching. The Co MOF achieves rapid electron exchange at the electrode electrolyte interface through this synergistic effect, improving conductivity, and increasing specific surface area, exposing more active sites, effectively enhancing the electrochemical activity of the electrode. Therefore, the e-Fe-doped Co MOF-4 h has a high specific capacity of 700 C g−1 at 1 A g−1 with a 90.08 % high-rate performance. The assembled e-Fe-doped Co MOF-4 h//N-doped WC ASC provides the energy density of 80 Wh kg−1 at a power density of 800 W kg−1 with a ∼88 % capacitance retention after 10000 cycles. These results provide ideas for utilizing synergistic effects to prepare high-energy density supercapacitors using MOF materials.

Single-Crystal P2-Na0.67Mn0.67Ni0.33O2 Cathode Material with Improved Cycling Stability for Sodium-Ion Batteries.

Layered oxides constitute one of the most promising cathode materials classes for large-scale sodium-ion batteries because of their high specific capacity, scalable synthesis, and low cost. However, their practical use is limited by their low energy density, physicochemical instability, and poor cycling stability. Aiming to mitigate these shortcomings, in this work, we synthesized polycrystalline (PC) and single-crystal (SC) P2-type Na0.67-δMn0.67Ni0.33O2 (NMNO) cathode materials through a solid-state route and evaluated their physicochemical and electrochemical performance. The SC-NMNO cathode with a large mean primary particle size (D50) of 12.7 μm was found to exhibit high cycling stability leading to 47% higher capacity retention than PC-NMNO after 175 cycles at 1C rate in the potential window 4.2-1.5 V. This could be attributed to the effective mitigation of parasitic side reactions at the electrode-electrolyte interface and suppressed intergranular cracking induced by anisotropic volume changes. This is confirmed by the lower volume variation of SC-NMNO (ΔV ∼ 1.0%) compared to PC-NMNO (ΔV ∼ 1.4%) upon charging to 4.2 V. Additionally, the SC-NMNO cathode displayed slightly higher thermal stability compared to PC-NMNO. Both cathodes exhibited good chemical stability against air and water exposure, thus enabling material storage/handling in the ambient atmosphere as well as making them suitable for aqueous processing. In this regard, PC-NMNO was investigated with two low-cost aqueous binders, carboxymethyl cellulose, and sodium trimetaphosphate, which exhibited higher binding strength and displayed excellent electrochemical performance compared to PVDF, which could potentially lead to significant cost reduction in electrode manufacturing.

The Optimal Doping Ratio of Fe2O3 for Enhancing the Electrochemical Stability of Zeolitic Imidazolate Framework-8 for Energy Storage Devices

This paper aims to discover a novel composite material that has great potential for manufacturing high-performance supercapacitors suitable for diverse applications, such as electric vehicles, portable electronics, and stationary energy storage systems. Zeolitic imidazolate framework-8 (ZIF-8) doped by different concentrations up to 5 wt.% of nanosized Fe2O3 have been prepared (ZIF-8/Fe2O3). The effect of doping ratio 1, 3, and 5 wt.% on the structural and electrochemical properties of ZIF-8/Fe2O3 has been investigated. The structural characterization has been carried out using TGA, BET, XRD, and FTIR. The XRD analysis revealed that the crystalline size of our sample increased by approximately 16% as a result of doping ZIF-8 with 5 wt.% of Fe2O3. The structural analysis of the doped samples revealed that the material exhibited enhanced thermal stability and porosity, with an increase of approximately 105 m2/g. The introduction of doped nanometal oxides improved the capacitance value of ZIF-8 by significantly increasing its surface area. Additionally, the electron transport efficiency within ZIF-8/5 wt.% Fe2O3/electrode is increased. The Nyquist plot decreases as the doping of Fe2O3 increases. This indicates a decrease in the charge transfer resistance at the electrode–electrolyte interface, which is desired in applications such as batteries, fuel cells, or electrochemical sensors where faster electron transfer is needed for improved performance.

Understanding wetting behavior in electrode–electrolyte interface formation and its sensitivity to electrode-current collector interaction: a lattice Boltzmann method approach

Understanding wetting behavior in electrode–electrolyte interface formation and its sensitivity to electrode-current collector interaction: a lattice Boltzmann method approach

Electrode Spacing Effects on the Capacitance of Glassy Carbon Electrodes in Aqueous Electrolytes

Abstract Matched glassy carbon electrodes in aqueous K2SO4 electrolytes were used to examine the effects of opposing electrode spacing on capacitive performance. Planar non-porous glassy carbon electrodes were used to avoid complications with porosity and roughness. Electrode spacing effects were examined in terms of device and individual electrode performance, using cyclic voltammetry, coupled with its deconvolution into residual, diffusional, and capacitive processes. Decreasing the spacing between electrodes led to a decrease in capacitive contributions, and a relative increase in diffusional and residual contributions, implying that individual electrodes were influencing the behaviour of each other. This is also consistent with the use of more dilute electrolytes. Electrode behaviour was modelled using the Poisson-Boltzmann equation, together with its integrated outputs of electric field and potential difference. For electrodes with the same amount of charge and a similar diffuse layer thickness, the electric field and potential drop was diminished because of their charge interaction. Conversely, it is shown that for a similar potential drop across the electrodes, the variable controlled in a cyclic voltammetry experiment, more charge accumulation is needed at the electrode-electrolyte interface to compensate for the counter charge generate from the opposing electrode.

Anion-Reinforced Solvation Structure Enables Stable Operation of Ether-Based Electrolyte in High-Voltage Potassium Metal Batteries.

Electrolytes with anion-dominated solvation are promising candidates to achieve dendrite-free and high-voltage potassium metal batteries. However, it's challenging to form anion-reinforced solvates at low salt concentrations. Herein, we construct an anion-reinforced solvation structure at a moderate concentration of 1.5 M with weakly coordinated cosolvent ethylene glycol dibutyl ether. The unique solvation structure accelerates the desolvation of K+, strengthens the oxidative stability to 4.94 V and facilitates the formation of inorganic-rich and stable electrode-electrolyte interface. These enable stable plating/stripping of K metal anode over 2200 h, high capacity retention of 83.0% after 150 cycles with a high cut-off voltage of 4.5 V in K0.67MnO2//K cells, and even 91.5% after 30 cycles under 4.7 V. This work provides insight into weakly coordinated cosolvent and opens new avenues for designing ether-based high-voltage electrolytes.

Rational design of low interfacial resistance between NiS2 cathode and electrolyte for high-performance Li thermal battery

As one of the main components of the cathode and electrolyte for Li thermal batteries (LTBs), conventional binders typically employ high thermal stability MgO to maintain LTBs structure stability, but MgO has the disadvantage of high resistance, which can result in a high resistance at the cathode-electrolyte interface. Thus, it is crucial to optimize the cathode-electrolyte interface for NiS2 to achieve high performance LTBs. Herein, Li7La3Zr2O12 (LLZO) with high thermal stability and excellent ionic conductivity was adopted in the cathode and electrolyte to replace the conventional binders, aiming to build a low resistance interface between the cathode and electrolyte, promoting the Li+ transport kinetics. More importantly, LLZO also plays a vital role in reducing molten salt leakage and enhancing the stability of the cathode-electrolyte interface in LTBs, which contributed to increasing the discharge capacity of the NiS2 cathode material. Consequently, LTB containing LLZO delivers a high discharge specific capacity of 635.1 mAh g−1 with a cut off voltage of 1.4 V at 100 mA cm−2 at 500 °C, retaining 72.8 % of the theoretical capacity of NiS2, which is 25.5 % higher than LTB with MgO. These findings indicate that optimizing the NiS2 electrode and LLZO electrolyte interface would be an effective way to enhance the performance of LTBs.

Uncovering the cation effects on the electroreduction of CO2 on Pd/C catalysts − an SEIRAS study

Electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) has long been known to be affected by the electrolyte cations, yet the interpretations of these effects remain controversial. In this work, taking advantage of the unique catalytic characteristics of Pd, we investigated the cation effects on the CO2RR. It was found that the productions of formate and carbon monoxide (CO) are accelerated, and the competitive hydrogen evolution reaction (HER) is suppressed on Pd surfaces by larger cations. Detailed ATR-SEIRAS measurements revealed the promotion of CO2RR comes from two aspects. First, the CO2 molecules can be concentrated at the electrode–electrolyte interface by larger cations through electrostatic interaction. Second, a stronger interfacial electric field brought by the larger cations can accelerate the CO2RR and stabilize the negatively charged intermediates. The potential-dependent spectral transitions of adsorbed CO and interfacial water shed new light on the cation-dependent electric double layer structures. In light of these findings, the cation effects on the formate and CO pathways at different overpotentials were further revealed.

Magnetic field based finite element method for magneto-static problems with discontinuous electric potential distributions

We introduce two finite element formulations to approximate magneto-static problems with discontinuous electric potential based respectively on the electrical scalar potential and the magnetic field. This work is motivated by our interest in Liquid Metal Batteries (LMBs), a promising technology for storing intermittent renewable sources of energy in large scale energy storage devices. LMBs consist of three liquid layers stably stratified and immiscible, with a light liquid metal on top (negative electrode), a molten salt in the middle (electrolyte) and a heavier liquid metal on bottom (positive electrode). Energy is stored in electrical potential differences that can be modeled as jumps at each electrode-electrolyte interface. This paper focuses on introducing new finite element methods for computing current and potential distributions, which account for internal voltage jumps in liquid metal batteries. Two different formulations that use as primary unknowns the electrical potential and magnetic field, respectively, are presented. We validate them using various manufactured test cases, and discuss their applications for simulating the current distribution during the discharge phase in a liquid metal battery.

Controllable Regulation of the Oxygen Redox Process in Lithium-Oxygen Batteries by High-Configuration-Entropy Spinel with an Asymmetric Octahedral Structure.

Designing bifunctional electrocatalysts to boost oxygen redox reactions is critical for high-performance lithium-oxygen batteries (LOBs). In this work, high-entropy spinel (Co0.2Mn0.2Ni0.2Fe0.2Cr0.2)3O4 (HEOS) is fabricated by modulating the internal configuration entropy of spinel and studied as the oxygen electrode catalyst in LOBs. Under the high-entropy atomic environment, the Co-O octahedron in spinel undergoes asymmetric deformation, and the reconfiguration of the electron structure around the Co sites leads to the upward shift of the d-orbital centers of the Co sites toward the Fermi level, which is conducive to the strong adsorption of redox intermediate LiO2 on the surface of the HEOS, ultimately forming a layer of a highly dispersed Li2O2 thin film. Thin-film Li2O2 is beneficial for ion diffusion and electron transfer at the electrode-electrolyte interface, which makes the product easy to decompose during the charge process, ultimately accelerating the kinetics of oxygen redox reactions in LOBs. Based on the above advantages, HEOS-based LOBs deliver high discharge/charge capacity (12.61/11.72 mAh cm-2) and excellent cyclability (424 cycles). This work broadens the way for the design of cathode catalysts to improve oxygen redox kinetics in LOBs.

Enhanced prelithiation performance of Li5FeO4 cathode additive and optimized solid electrolyte interface enabled by Mn substitution

In the pursuit of enhancing the energy density of lithium-ion batteries, cathode prelithiation emerges as a pivotal approach, introducing additional irreversible active lithium ions to augment performance. Li5FeO4 (LFO) stands out as an excellent option, boasting an impressive theoretical specific capacity and the additional advantages of cost-effectiveness in raw materials and low preparation cost. However, the impact of extra lithium incorporations on compositional changes at the electrode-electrolyte interface as well as on cell stability has impeded further researches. Herein, a Mn doping strategy is proposed and predicted by first-principles calculations to synthesize partially Mn-substituted Li5.125Fe0.875Mn0.125O4 (LFMO). And the prelithiation with LFMO improved the interfacial composition of LiFePO4 (LFP) batteries compared to LFO, achieving a charging capacity of 213 mAh∙g−1 in the first cycle at 0.05 C. The subsequent treatment demonstrated superior cycling stability, maintaining a discharge specific capacity as high as 155.3 mAh∙g−1 after 100 cycles at 0.2 C, and exhibiting a higher capacity retention in the full cell. These discoveries could contribute to enhancing the regulation of battery interface during the utilization of LFO, potentially promoting the development of cathode lithium additives.

Fast Room‐Temperature Mg‐Ion Conduction in Clay‐Like Halide Glassy Electrolytes

AbstractThe discovery of mechanically soft solid‐state materials with fast Mg‐ion conduction is crucial for the development of solid‐state magnesium batteries. In this paper, novel magnesium gallium halide compounds are reported that achieve high ionic conductivity of 0.47 mS cm−1 at room temperature. These Mg‐ion conductors obtained by ball milling Mg and Ga salts exhibit clay‐like mechanical properties, enabling intimate contact at the electrode–electrolyte interface during battery cycling. With a combination of experimental and computational analysis, this study identifies that the soft‐clay formation is induced by partial anion exchange during milling. This partial anion exchange creates undercoordinated magnesium ions in a chlorine‐rich environment, yielding fast Mg‐ion conduction. This work demonstrates the potential of clay‐like halide electrolytes for all‐solid‐state magnesium batteries, with possible further extension to other multivalent battery systems.

LiTaO3 mixing effects to suppress side reactions at the LiNi0.8Co0.1Mn0.1O2 cathode and Li5.3PS4.3Cl1.7 solid electrolyte of all-solid-state lithium batteries

Suppressing the side reactions at the solid electrolyte-electrode interface in all-solid-state battery (ASSB) is very important aspect of improving battery performance. Coating an electrochemically stable material on the surface of cathode has been used to suppress the side reactions occurring at interface between solid electrolyte and cathode. However, to achieve effective suppression, the thickness of the coating film must be thin and uniform. Moreover, an expensive ethoxide series typically must be used as a starting material. In this study, LiTaO3 coating material was simply mixed with the solid electrolyte to measure the effect of suppressing side reactions. To synthesize the solid electrolyte Li5.3PS4.3Cl1.7 and the mixing material LiTaO3, high-energy ball milling and wet milling methods were used, respectively. The structural characteristics of the prepared solid electrolytes were studied by powder X-ray diffraction. The LiTaO3 mixed solid electrolyte based ASSB showed a high discharge capacity of 177.3 mAh/g in the initial cycle, whereas the bare solid electrolyte (Li5.3PS4.3Cl1.7) based ASSB showed a discharge capacity of 159.1 mAh/g. To understand the side reactions, electrochemical impedance spectroscopy (EIS) analysis was performed after galvanostatic charge-discharge cycles. The EIS analysis confirmed that the side reaction between a solid electrolyte and a cathode was effectively suppressed in LiTaO3 mixed solid electrolyte based ASSBs.

Electrolyte design to regulate the electrode–electrolyte interface on the electrochemical performance for K0.5MnO2||graphite-based potassium-ion batteries

The system of layered-metal-oxide||carbon-anode cells with carbonate electrolytes is highly promising for constructing potassium-ion batteries (PIBs). However, this system faces serious issues of poor compatibility between the electrolyte and electrode, particularly with conventional ethylene carbonate (EC)-based electrolytes. Herein, owing to the regulated coordination environment of cation–anion-solvent and the formed KF-rich interface, a superior rate performance of graphite anode was achieved. The designed 4 M KFSI EC/DEC electrolyte demonstrates superior performance in graphite||K cells, exhibiting a high reversible capacity of approximately 200 mAh g−1 at a high current density of 700 mA g−1, surpassing many reported high-concentration and weak solvation PIB electrolytes. Meanwhile, it exhibits low polarization and maintains stable contact stability with active K metal. Furthermore, it demonstrates great compatibility with Mn-based layered metal oxide cathodes. Remarkably, we reveal a unique formation mechanism of the solvent-anion co-derived solid electrolyte interface (SEI) through a two-stage XPS deep analysis, which has the KF-deficient inorganic inner and KF-rich outer. This SEI can protect the graphite structure and enable great rate performance of graphite anode. This work holds significant reference value for the design of commercial electrolytes.

Unraveling the Evolution of Dynamic Active Sites of LaNixFe1-xO3 Catalysts During OER.

Perovskites have attracted tremendous attention as potential catalysts for the oxygen evolution reaction (OER). It is well-known that the introduction of Fe into rare earth perovskites such as LaNiO3 enhances the intrinsic OER activity. Despite numerous studies on structure-property relationships, the origin of the activity and the nature of the active species are still elusive and unclear. In this work, we study a series of LaNixFe1-xO3 perovskites using in situ electrochemical surface-enhanced Raman spectroscopy and electron energy loss spectroscopy to decipher the surface evolution and formation of active species during OER. While the origin of the activity arises from NiOOH species formed from the active Ni centers in LaNiO3, our work shows that Fe serves as the active center in LaNi0.5Fe0.5O3 and forms Fe-O-Ni and FeOOH species during OER. The OER activity of LaFeO3 originates from FeOOH species, which interact with the soluble Ni species in the electrolyte forming an active electrode-electrolyte interface with high-valent stable surface iron species (Fe4+) and thereby improving the performance. Our work provides deeper insights into the synergistic effects of Ni and Fe on the catalytic activity, which in turn provides new design principles for perovskite catalysts for the OER.

Unraveling the Roles of Dissolved Mn(2+) and Its Impact on the Electrode–Electrolyte Interface under Realistic Conditions

Unraveling the Roles of Dissolved Mn(2+) and Its Impact on the Electrode–Electrolyte Interface under Realistic Conditions

Steering Selectivity in Electrocatalytic Furfural Reduction via Electrode-Electrolyte Interface Modification.

Electrocatalytic reduction of biomass-derived furfural (FF) represents a sustainable route to produce furfuryl alcohol (FA) and 2-methylfuran (MF) as a value-added chemical and a biofuel, respectively. However, achieving high selectivity for MF as well as tuning the selectivity between FA and MF within one reaction system remain challenging. Herein, we have reported an electrode-electrolyte interface modification strategy, enabling FA and MF selectivity steering under the same reaction conditions. Specifically, by modifying copper (Cu) electrocatalysts with butyl trimethylammonium bromide (BTAB), we achieved a dramatic shift in selectivity from producing FA (selectivity: 83.8%; Faradaic efficiency, FE: 68.9%) to MF (selectivity: 80.1%; FE: 74.8%). We demonstrated that BTAB adsorption over Cu modulates the electrical double layer (EDL) structure, which repels interfacial water and weakens the hydrogen-bond (H-bond) network for proton transfer, thus impeding FF-to-FA conversion by suppression of the hydrogen atom transfer (HAT) process. On the contrary, FF-to-MF conversion was less affected. This work shows the potential of engineering of the electrode-electrolyte interface for selectivity control in electrocatalysis.

Achieving Dendrite-Free Zinc Metal Anodes via Molecule Anchoring and lon-Transport pumping.

The potential for scale-up application has been acknowledged by researchers for rechargeable aqueous zinc-ion batteries (ZIBs). Nonetheless, the progress of the development is significantly impeded due to the instability of the interface between the zinc anode and electrolyte. Herein, efficient and environmentally benign valine (Val) were introduced as aqueous electrolyte additive to stabilize the electrode/electrolyte interface (EEI) via functional groups in additive molecules, thus achieving reversible dendrite-free zinc anode. The amino groups present in Val molecules have a strong ability to adsorb on the surface of zinc metal, enabling the construction of anchored molecular layer on the surface of zinc anodes. The strongly polar carboxyl groups in Val molecules can act as ion-transport pumps to capture zinc ions in the electric double layer (EDL) through coordination chemistry. Therefore, this reconstructed EEI could modulate the zinc ion flux and simultaneously suppress side reactions and dendritic growth of Zn. Consequently, a long stable cycling up to 1400 h at a high current density of 20 mA cm-2 is achieved. Additionally, Zn//V2O5 full cell with Val additive exhibit enhanced cyclability, retaining 77 % capacity after 3000 cycles, displaying significant potential in promoting the commercialization of ZIBs.