Additive-free Electrolyte Research Articles

Impact of Jellyroll Tapes on Performance of Layered Oxide/Hard Carbon Sodium-Ion Pouch Cells

This study investigates the influence of jellyroll tape materials on the cycle life and self-discharge of layered oxide/hard carbon sodium-ion pouch cells. Jellyroll tapes made of polyethylene terephthalate (PET) or polypropylene (PP) polymer were used in this study. Severe PET tape decomposition was observed in additive-free electrolyte. The use of solid-electrode interphase forming additives suppressed PET tape decomposition effectively and resulted in a competitive performance comparable to that of cells with PP tape. Replacing PET tape with PP tape led to sodium-ion pouch cells with substantial improvements of capacity retention, coulombic efficiency, and charge endpoint slippage. The superior chemical stability of PP tape in sodium-ion batteries allows for long cycle life and low self-discharge even in the absence of additives.

Zn-anode stability in additive added perchlorate electrolyte for aqueous Zn-MnO2 battery

Extensive research has been conducted on aqueous Zn-MnO2 batteries in the most common ZnSO4 electrolyte. However, the present study focuses on Zn anode stability and subsequent pairing with the commonly utilized MnO2 cathode in a low-concentration aqueous Zn (ClO4)2 electrolyte containing an organic additive, triethyl phosphate (TEP). The structural stability of Zn anodes in optimized additive-added and additive-free electrolytes is analyzed by assembling series of Zn∥Zn symmetry cells under various electrochemical conditions with varying depth of discharges between 20 and 60 %. As such, additive added electrolyte stabilizes the Zn anode over 250 h under high areal capacity/low areal current density of 38.3 mAh cm−2/11.3 mA cm−2 with 60 % depth of discharge at long half-cycle time of 29.5 h. The Zn-MnO2 paired cells in the Zn (ClO4)2 electrolyte with and without additives registered reversible capacities of 262 and 247 mAh g−1, respectively, at 0.05 A g−1. These electrochemical features are completely different from those of the common ZnSO4 electrolyte, whose electrochemical mechanism is still a subject of debate.

Insight into Fluoride Additives to Enhance Ammonia Production from Lithium-Mediated Electrochemical Nitrogen Reduction Reaction.

Demands for green ammonia production increase due to its application as a proton carrier, and recent achievements in electrochemical Li-mediated nitrogen reduction reactions (Li-NRRs) show promising reliability. Here, it is demonstrated that F-containing additives in the electrolyte improve ammonia production by modulating the solid electrolyte interphase (SEI). It is suggested that the anionic additives with low lowest unoccupied molecular orbital levels enhance efficiency by contributing to the formation of a conductive SEI incorporated with LiF. Specifically, as little as 0.3wt.% of BF4 - additive to the electrolyte, the Faradaic efficiency (FE) for ammonia production is enhanced by over 15% compared to an additive-free electrolyte, achieving a high yield of 161 ± 3nmol s-1 cm-2. The BF4 - additive exhibits advantages, with decreased overpotential and improved FE, compared to its use as the bulk electrolyte. The observation of the Li3N upper layer implies that active Li-NRR catalytic cycles are occurring on the outermost SEI, and density functional theory simulations propose that an SEI incorporated with LiF facilitates energy profiles for the protonation by adjusting the binding energies of the intermediates compared to bare copper. This study unlocks the potential of additives and offers insights into the SEIs for efficient Li-NRRs.

Microcapsule Modification Strategy Empowering Separator Multifunctionality to Enhance Safety of Lithium-Metal Batteries.

The uncontrollable growth of lithium dendrites and the flammability of electrolytes are the direct impediments to the commercial application of high-energy-density lithium metal batteries (LMBs). Herein, this study presents a novel approach that combines microencapsulation and electrospinning technologies to develop a multifunctional composite separator (P@AS) for improving the electrochemical performance and safety performance of LMBs. The P@AS separator forms a dense charcoal layer through the condensed-phase flame retardant mechanism causing the internal separator to suffocate from lack of oxygen. Furthermore, it incorporates a triple strategy promoting the uniform flow of lithium ions, facilitating the formation of a highly ion-conducting solid electrolyte interface (SEI), and encouraging flattened lithium deposition with active SiO2 seed points, considerably suppressing lithium dendrites growth. The high Coulombic efficiency of 95.27% is achieved in Li-Cu cells with additive-free carbonate electrolyte. Additionally, stable cycling performance is also maintained with a capacity retention rate of 93.56% after 300 cycles in LFP//Li cells. Importantly, utilizing P@AS separator delays the ignition of pouch batteries under continuous external heating by 138s, causing a remarkable reduction in peak heat release rate and total heat release by 23.85% and 27.61%, respectively, substantially improving the fire safety of LMBs.

The Construction of Anion-Induced Solvation Structures in Low-concentration Electrolyte for Stable Zinc Anodes.

Aqueous zinc-ion batteries (ZIBs) are promising large-scale energy storage devices because of their low cost and high safety. However, owing to the high activity of H2O molecules in electrolytes, hydrogen evolution reaction and side reactions usually take place on Zn anodes. Herein, additive-free PCA-Zn electrolyte with capacity of suppressing the activity of free and solvated H2O molecules was designed by selecting the cationophilic and solventophilic anions. In such electrolyte, contact ion-pairs and solvent-shared ion-pairs were achieved even at low concentration, where PCA- anions coordinate with Zn2+ and bond with solvated H2O molecules. Simultaneously, PCA- anions also induce the construction of H-bonds between free H2O molecules and them. Therefore, the activity of free and solvated H2O molecules is effectively restrained. Furthermore, since PCA- anions possess a strong affinity with metal Zn, they can also adsorb on Zn anode surface to protect Zn anode from the direct contact of H2O molecules, inhibiting the occurrence of water-triggered side reactions. As a result, plating/stripping behavior of Zn anodes is highly reversible and the coulombic efficiency can reach to 99.43 % in PCA-Zn electrolyte. To illustrate the feasibility of PCA-Zn electrolyte, the Zn||PANI full batteries were assembled based on PCA-Zn electrolyte and exhibited enhanced cycling performance.

Unveiling the potential of redox electrolyte additives in enhancing interfacial stability for Zn-ion hybrid capacitors

Zinc-ion hybrid capacitors (ZICs) that combine the characteristics of metal-ion batteries and supercapacitors are emerging to fulfill high energy-power demands. The objective of this study is to address the challenges in the practical implementation of metallic zinc for ZICs. In this work, we explore redox molecules based on anthraquinone compounds as electrolyte additives for the interfacial engineering of Zn anodes. The results reveal that the additives enable favorable solvation of Zn2+ through metal ion-ligand coordination. The redox additives improve the lifespan of Zn//Zn cells from 50 to 1600 cycles at 2 mA cm−2 and 1 mAh cm−2 due to the suppression of parasitic reactions and the mitigation of by-product formations. The redox properties of additives strengthen the pseudocapacitive behavior of the ZICs, enabling efficient interfacial charge and mass transfer. The redox-enhanced device manifests an increased capacity of 195.0 mAh g − 1 with improved cycling stability, compared to that of 149.6 mAh g − 1 for the additive-free electrolyte. The universal strategy, based on the synergistic effects of redox additives, is demonstrated by a collection of molecules with similar structures. This work unveils a conceptually new approach that utilizes redox additives to formulate advanced electrolytes for aqueous energy storage.

Electrodeposition of stress-relaxation-induced (111)-oriented nanotwin copper film by direct current in additive-free electrolyte

In this study, we investigated the electrodeposition of stress-induced (111)-oriented nanotwin copper films using direct current in an additive-free electrolyte. We aimed to explore the effects of temperature, current density, and agitation on the formation of nanotwins. At lower temperatures, (111) orientation was induced due to the decrease in adatom surface diffusion. Additionally, higher current densities, which induced high initial residual stress, promoted the formation of (111)-oriented nanotwins, resulting in stress relaxation and a reduction in residual stress. Agitation had a negligible effect on nanotwin formation in our experiments, which were conducted in the additive-free electrolyte. Our findings provide valuable insights into the controlled formation of (111)-oriented nanotwin Cu films and their potential applications in fields requiring Cu films with superior mechanical and electrical properties, which are improved by the formation of nanotwins. By comprehending the fundamental mechanisms involved, it becomes possible to optimize electrodeposition processes for (111)-oriented nanotwin copper films.

Super-flat and uni-oriented cobalt film electrodeposited by modulating the crystal nucleation and growth behavior

A precise control of the microstructure of electrodeposited cobalt film is crucial for attaining the desired and reproducible electrical performance in edge nanoelectronic devices. Here we realize the super-flat and uni-oriented cobalt film through a one-step electrodeposition process using benzenesulfinic acid (BNS) as additive. We find that the unsaturated sulfite group in BNS plays a key role in the super-flat cobalt electroplating. Molecular activity analysis and electrochemical test results suggested that the electron donating ability of the sulfite group was higher than that of the sulfonate group, resulting in stronger adsorption of BNS on the cobalt surface and enhanced cathodic polarization. Nucleation model fitting and surface morphology evolution studies revealed that the cobalt nucleation with BNS shifted to progressive nucleation from instantaneous nucleation in the additive-free electrolyte, leading to a more uniform and compact film morphology. Furthermore, equilibrium adsorption calculations indicated that the selective and strong adsorption of BNS on cobalt planes was responsible for the preferential orientation of the (002) crystal plane growth. After annealing, cobalt films prepared with BNS exhibited substantial grain growth and impurity diffusion, which further improved the electrical performance.

Shuttling-free redox electrolyte locks proton-conductive polyoxometalates in porous carbon for high-performance pseudocapacitors

Redox electrolytes are highly attractive to bring conventional carbon-based supercapacitors the additional pseudocapacitance; however, shuttling of redox species remains a severe issue restricting the potential applications of redox electrolytes. Here, we report a new phosphotungstic acid-containing redox electrolyte for carbon-based supercapacitors, which shows the shuttling-free feature by locking the polyoxometalate mediators in the porous carbon electrode. Impressively, the porous carbon electrode affords a remarkable specific capacitance of 885.7 F g−1 at 5 mV s−1 in the phosphotungstic acid-added electrolyte, triple that in the additive-free H2SO4 electrolyte (290.2 F g−1). Profiting from the unique Grotthuss proton conduction of phosphotungstic acid, the porous carbon electrode achieves the dramatic rate capability in our redox electrolyte (i.e., 567.7 F g−1 at 200 mV s−1). Moreover, the assembled supercapacitor device affords a specific energy of 52.3 Wh kg−1 and long-term cycling stability (93.7% over 5000 cycles). This study highlights the superiority of the polyoxometalate additive for redox electrolytes in developing advanced supercapacitors integrating high energy density, excellent rate performance, and electrochemical durability.

Catalytic Chemistry Derived Artificial Solid Electrolyte Interphase for Stable Lithium Metal Anodes Working at 20 mA cm-2 and 20 mAh cm-2.

A stable solid electrolyte interphase (SEI) layer is crucial for lithium metal anode (LMA) to survive in long-term cycling. However, chaotic structures and chemical inhomogeneity of natural SEI make LMA suffering from exasperating dendrite growth and severe electrode pulverization, which hinder the practical application of LMAs. Here, we design a catalyst-derived artificial SEI layer with an ordered polyamide-lithium hydroxide (PA-LiOH) bi-phase structure to modulate ion transport and enable dendrite-free Li deposition. The PA-LiOH layer can substantially suppress the volume changes of LMA during Li plating/stripping cycles, as well as alleviate the parasitic reactions between LMA and electrolyte. The optimized LMAs demonstrate excellent stability in Li plating/stripping cycles for over 1000 hours at an ultra-high current density of 20 mA cm-2 in Li||Li symmetric cells. A high coulombic efficiency up to 99.2 % in Li half cells in additive-free electrolytes is achieved even after 500 cycles at a current density of 1 mA cm-2 with a capacity of 1 mAh cm-2 .

Reversible Magnesium Metal Cycling in Additive-Free Simple Salt Electrolytes Enabled by Spontaneous Chemical Activation.

Rechargeable magnesium (Mg) batteries can offer higher volumetric energy densities and be safer than their conventional counterparts, lithium-ion batteries. However, their practical implementation is impeded due to the passivation of the Mg metal anode or the severe corrosion of the cell parts in conventional electrolyte systems. Here, we present a chemical activation strategy to facilitate the Mg deposition/stripping process in additive-free simple salt electrolytes. By exploiting the simple immersion-triggered spontaneous chemical reaction between reactive organic halides and Mg metal, the activated Mg anode exhibited an overpotential below 0.2 V and a Coulombic efficiency as high as 99.5% in a Mg(TFSI)2 electrolyte. Comprehensive analyses reveal simultaneous evolution of morphology and interphasial chemistry during the activation process, through which stable Mg cycling over 990 cycles was attained. Our activation strategy enabled the efficient cycling of Mg full-cell candidates using commercially available electrolytes, thereby offering possibilities of building practical Mg batteries.

Combining 3D Printing and Electrochemical Deposition for Manufacturing Tailor-Made 3D Nickel Foams with Highly Competitive Porosity and Specific Surface Area Density

One of the most promising and heavily researched energy storage systems due to their high energy density, rate capability and extended cycle life are lithium-ion batteries. Their performance and efficiency are nonetheless strongly dependent on their constituent materials and design, including the current collectors. One attractive approach in this respect is the use of metal foams as an alternative to the conventional current collectors. This concept is therefore intended to increase the current collectors’ specific surface area and therefore load more active material by nominal area while keeping the cell architectures simple and less costly. In the present work, nickel is chosen as a model system for a proof of concept of a novel manufacturing method for nickel foams using a combination of 3D printing, coating and electroplating. The purpose is to create geometrically well-defined hollow structures with high porosity and specific surface area density that can rival and partially outperform the commercially available nickel foams. To this end, a 3D printer is used to create geometrically flexible and well-defined open-pored disks of HIPS (high-impact polystyrene), which are then spray coated with a graphite-based conducting layer and subsequently electroplated with a 5–30 µm thin layer of nickel from an additive-free nickel sulfamate electrolyte. Following the coating process, the support structure is dissolved with toluene, resulting in structures with a unique combination of porosity in the range of 92.3–99.1% and an ultra-high specific surface area density up to 46 m2/kg. Morphological characterization by light and scanning electron microscopy has proven that the temporarily required polymer substrate can be mildly and completely removed by the suggested room temperature dissolution process.

Increased cycling rates for thick all active material electrodes via electrolyte modifications

Lithium-ion (Li-ion) batteries are the dominant energy storage technology in many applications due to high energy and power density, and research efforts continue towards further advances in their electrochemical properties. One general strategy to increase energy density at the cell level is to increase electrode thickness. However, with increased electrode thickness and loading, ionic transport becomes a limiting factor. All active material (AAM) electrodes provide a route to increase electrode thickness without inactive conductive additives and polymer binders, which results in relative ionic transport advantages due to the absence of these inactive materials in the electrode interstitial regions. AAM electrodes processed herein have mildly sintered LiFePO4 (LFP) and Li4Ti5O12 (LTO) fabricated into AAM electrodes as cathode and anode. These materials were paired and combined with electrolyte systems with solvent additives which increased electrolyte ionic conductivity. The resulting cells had high areal capacities, and the capacity achieved at increasing current density was significantly improved relative to the additive-free electrolyte which was attributed to the improved ionic conductivity with the electrolyte additives.

Nucleation-controlled growth of Cu thin films electrodeposited directly on ALD Ru diffusion barrier in additive-free electrolyte for Cu interconnect

Direct Cu electrodeposition on a 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer was investigated for Cu interconnect in Si-based microelectronic devices. A Cu-ammonia-citrate (Cu-NH3-Cit) electrolyte was employed with no additives. The nucleation behavior of Cu on Ru was dependent on the cathodic potential applied to ALD Ru/SiO2/Si wafer specimen whether it is instantaneous or progressive. Preferable instantaneous nucleation with a high area density of Cu nuclei on Ru contributed to the formation of uniform Cu thin films. Lastly, direct Cu electrodeposition onto Ru at a constant cathodic potential of −1.0 V filled 30-nm-wide and 120-nm-deep trenches with void-free Cu.

Solid–Electrolyte Interface Formation on Si Nanowires in Li-Ion Batteries: The Impact of Electrolyte Additives

The morphological changes of Si nanowires (Si NWs) cycled in 1:1 ethylene–carbonate (EC)/diethyl–carbonate (DEC) with or without different additives, fluoroethylene carbonate (FEC) or vinylene carbonate (VC), as well as the composition of the deposited solid–electrolyte interphase layer, are investigated by a combination of experimental microscopic and spectroscopic techniques. Scanning electron microscopy and optical spectroscopy highlight that the NW morphology is better preserved in samples cycled in the presence of FEC and VC additives compared to the additive-free electrolyte. However, only the use of FEC is capable of slightly mitigating the amorphization of silicon upon cycling. The solid electrolyte interphase (SEI) formed over the Si NWs cycled in the additive-free electrolyte is richer in organic and inorganic carbonates compared to the SEI grown in the presence of the VC and FEC additives. Furthermore, both additives are able to remarkably limit the degradation of the LiPF6 salt. Overall, the use of the FEC-additive in the carbonate-based electrolyte promotes both morphological and structural resilience of the Si NWs upon cycling thanks to the optimal composition of the SEI layer.

Enhancement of the Na2FePO4F@gC3N4 electrochemical performance in view of its implementation in sodium-ion batteries

Na2FePO4F fluorophosphate has long been regarded as potential cathode material for sodium-ion batteries (SIBs) due to its undeniable economic and environmental advantages. Herein, the preparation of Na2FePO4F powder using an easier and cost-effective technique is reported. The prepared compound, using phosphoric acid as P-source, crystallizes in an orthorhombic structure with the Pbcn space group as confirmed by X-Ray Diffraction (XRD) analysis. The pristine material (refers to as PM) is combined with different percentages of graphitic carbon nitride g-C3N4 as a carbon source (15% and 20%), to build large specific surfaces, boost electronic conductivity, and achieve the optimal carbon content. Raman spectrum reveals the existence of residual carbon denoting that the in-situ carbon coating process is successful. Thermogravimetric analysis (TGA) confirmed the stability of iron fluorophosphate at temperatures of 750 °C. Scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS) are used to investigate the materials' surface morphology and particle size. The performance of 15% and 20% g-C3N4 coated materials are tested as cathodes in both pure 1 M NaClO4 in polycarbonate electrolyte and in added 5% fluoroethylene carbonate electrolyte. High cycling properties and improved electrochemical performance were revealed when compared to the additive-free electrolyte.

Square-wave pulse electrodeposition of gold nanoparticles for ethanol electrooxidation

Gold nanoparticles with precisely controlled sizes for electrocatalyst in ethanol electrooxidation reaction were synthesized using a one-step square-wave pulse deposition technique in an additive-free electrolyte.

Differentiating contribution to desolvation ability from molecular structure and composition for screening highly-effective additives to boost reversibility of zinc metal anode

Optimizing aqueous electrolytes with additives is a practical strategy to postpone dendrite formation on Zn metal anode (ZMA) and therefore boost rechargeability of full zinc metal batteries (ZMBs). However, the fundamental screening principles of additives diverse in molecular structure and composition are still elusive. Herein, thiourea, urea, and allantoin are investigated as additives to regulate ZnSO4 baseline electrolyte. By combining systematical electrochemical measurements with detailed numerical simulation analysis, two fundamental principles for screening the additives with stronger desolvation ability toward hydrated zinc ions have been identified: (i) in molecular composition, carbonyl (urea) is better than thiocarbonyl (thiourea), and (ii) in molecular structure, bidentate coordination mode (allantoin) outperforms monodentate mode (urea). Consequently, an electrostripping/plating lifespan over 600 h in the Zn||Zn symmetric cell cycling under a depth of discharge up to 5.2% is realized with the optimum allantoin-ZnSO4 hybrid electrolyte, significantly boosting the rechargeability (85.7% capacity retention over 2000 cycles) of assembled ZMA||carbon-cloth@MnO2 full ZMBs than that with additive-free ZnSO4 electrolyte (40.5%). This work provides closer insights into the correlation between desirable dendrite-free behavior of ZMA and molecular characteristics of additives, and practical guidance for rational selection of more efficient additives to inhibit hydration of Zn2+ and suppress dendrite grown on ZMA.

Targeted leveling of the undercoordinated high field density sites renders effective zinc dendrite inhibition

Suppressing morphological instability during electrodeposition of zinc has lately been the subject of intense research owing to its significance for aqueous zinc-ion batteries with tremendous potential for renewable and grid storage applications. A variety of surface coating and electrolyte optimization approaches have been explored, but controlled leveling of undercoordinated zinc sites that are responsible for uneven dendritic deposition have never been considered. Here, the unique and targeted leveling action of two additives on two crystallographically distinct active Zn sites - on the corrugated {100}hexagonal facets of growing zinc crystallites and around surface irregularities, respectively - is unraveled through both theory and experiments, which enables compact and smooth deposition morphology conducive for stable cycling. An optimized ratio of the additives endows over 1200 h of Zn plating/stripping at 2 mA - 2 mAh cm−2, a 40-fold enhancement over the additive-free zinc sulfate electrolyte. Most importantly, the stability of the Zn cycling translates to the long-term full cell cyclability for a high cathode loading without affecting the obtainable capacity and rate performance. Fundamentally, this work reveals the unique mechanistic vantage of the additive functionality relative to the nature of the undercoordinated zinc site, critical to achieving comprehensive control over the zinc deposition morphology for durable cycling.

“In Situ” Formation of Zn Anode from Bimetallic Cu-Zn Alloy (Brass) for Dendrite-Free Operation of Zn-Air Rechargeable Battery

In this article, the performance of brass electrode was investigated in a Zn-air (charcoal-based cathode) rechargeable battery. The construction of the battery was carried out with biodegradable materials, namely a cotton cloth diaphragm and carboxymethyl cellulose sodium salt (CMC-Na) viscosity modifier, while the battery skeleton was printed by 3D printing technology. The brass acted as a collector and a preferable surface for the metallic Zn deposition on the brass anode surface. The electrochemical behavior of the brass anode was investigated by cyclic voltammetry (CV). Cyclic performance tests were carried out, which showed stable cell operation even in the presence or absence of additives up to more than 100 cycles. Furthermore, high energy (Eeff) and Coulomb (Ceff) efficiencies, 80% (Eeff), 95% (Ceff), 75% (Eeff), and 95% (Ceff) were obtained, respectively. The Shepherd model was applied to describe the discharging processes of the Zn-air battery containing brass as anode in the presence of additive-free electrolyte or electrolyte with CMC-Na salt additive. It was found that the Shepherd equation described only approximately the resulting discharge curves. In order to attain a more precise mathematical description, stretched exponential function was implemented into the last term of the Shepherd equation. The need for such a correction shows the complexity of the electrochemical processes occurring in these systems. In addition, the surface of the brass anode was also investigated by scanning electron microscopy (SEM) and the composition of the brass alloys was determined by X-ray fluorescence spectroscopy (XRF). Importantly, the formation of dendritic deposition was successfully suppressed and a smooth and uniform surface was obtained after the cycling tests.