Liquid Electrolyte Research Articles

Nanofillers modified with aluminum carboxylate for application in Polymer composite electrolytes for lithium-ion batteries

AbstractOne of the additives that positively influence the parameters of the electrolyte for lithium-ion cells are ceramic nanoparticles, such as SiO2 and α-Al2O3. However, they tend to agglomerate and sediment, which is an unfavorable phenomenon. An effective strategy to prevent this is to modify the surface of the particles with polymeric compounds, which can increase compatibility and stability in the electrolyte system. To reduce agglomeration and sedimentation, a method was developed to modify aluminum oxide and silica particles using aluminum carboxylate, which chemically combines with inorganic particles that have hydroxyl groups on their surface through an alkoxide bond. This method allows the introduction of oligooxyethylene groups to the ceramic surface, thus obtaining more stable systems. The effectiveness of this modification was confirmed through dynamic light scattering (DLS) measurements of particle size in liquid organic solvents, which are potential solvents for liquid electrolytes in lithium-ion cells. The modified nanosilica and aluminum oxide particles were then used as additives to solid polymer electrolytes made of poly(ethylene oxide) (PEO). This led to higher conductivity values compared to the use of unmodified fillers. The obtained values of lithium transference number for solid polymer electrolyte with PEO/CF3SO3Li and nanosilica or aluminum oxide modified with aluminum carboxylate are equal to 0.32–0.40.

Research Progress on Improvement Strategies of Polymer Electrolytes in Solid-State Batteries

The solid electrolyte material can replace the liquid electrolyte in the lithium-ion batteries, which ensures higher safety due to the flammable and corroded of liquid electrolyte. The polymer electrolytes demonstrated feasibility due to its suitable ductility. However, lithium ions in the polymer electrolytes are more difficult to ionize, resulting in worse ionic conductivity. At the same time, the mechanical strength of polymer electrolytes is not as good as that of inorganic electrolytes, which is not enough to inhibit the penetration of lithium dendrite. To solve these problems, researchers adopt two strategies: adding fillers or reactants and constructing artificial interface layers, focusing on improving ionic conductivity and mechanical strength. Based on the latest research, the problems faced by polymer electrolytes and improvement measures are reviewed, which provide references for the future development of polymer electrolytes.

Innovations in Energy Through Nanomaterials Enhancing Solid-State Battery Safety and Efficacy

The development of solid-state batteries (SSBs) represents a significant advancement in energy storage technology, addressing the limitations of traditional liquid electrolyte batteries, such as safety concerns and efficiency issues. However, SSBs face challenges including rigid solid-to-solid contacts, poor interfacial stability, and suboptimal performance across temperature ranges. This paper explores the role of nanotechnology in enhancing the performance and safety of SSBs. It highlights the applications of nanomaterials, such as nano-composites, nano-coatings, and embedded nanoparticles, which improve ionic conductivity, mechanical strength, and thermal management. The paper also discusses the challenges of commercializing nanotechnology in SSBs, including high production costs and regulatory hurdles. Despite these challenges, nanotechnology offers promising solutions for increasing the energy density and cycle life of SSBs, making them viable for applications in electric vehicles and consumer electronics. The paper concludes with recommendations for future research directions, emphasizing the need for continued innovation to fully realize the potential of SSBs in various industries.

Regulating Non‐Equilibrium Solvation Structure in Locally Concentrated Ionic Liquid Electrolytes for Wide‐Temperature and High‐Voltage Lithium Metal Batteries

AbstractThe development of high‐voltage lithium metal batteries (LMBs) encounters significant challenges due to aggressive electrode chemistry. Recently, locally concentrated ionic liquid electrolytes (LCILEs) have garnered attention for their exceptional stability with both Li anodes and high‐voltage cathodes. However, there remains a limited understanding of how diluents in LCILEs affect the thermodynamic stability of the solvation structure and transportation dynamics of Li+ ions. Herein, we propose a wide‐temperature LCILEs with 1,3‐dichloropropane (DCP13) diluent to construct a non‐equilibrium solvation structure under external electric field, wherein the DCP13 diluent enters the Li+ ion solvation sheath to enhance Li+ ion transport and suppress oxidative side reactions at high‐nickel cathode (LiNi0.9Co0.05Mn0.05O2, NCM90). Consequently, a Li/NCM90 cell utilizing this LCILE achieves a high capacity retention of 94 % after 240 cycles at 4.3 V, also operates stably at high cut‐off voltages from 4.4 V to 4.6 V and over a wide temperature range from −20 °C to 60 °C. Additionally, an Ah‐level pouch cell with this LCILE simultaneously achieves high‐energy‐density and stable cycling, manifesting the practical feasibility. This work redefines the role of diluents in LCILEs, providing inspiration for electrolyte design in developing high‐energy‐density batteries.

Regulating Non-Equilibrium Solvation Structure in Locally Concentrated Ionic Liquid Electrolytes for Wide-Temperature and High-Voltage Lithium Metal Batteries.

The development of high-voltage lithium metal batteries (LMBs) encounters significant challenges due to aggressive electrode chemistry. Recently, locally concentrated ionic liquid electrolytes (LCILEs) have garnered attention for their exceptional stability with both Li anodes and high-voltage cathodes. However, there remains a limited understanding of how diluents in LCILEs affect the thermodynamic stability of the solvation structure and transportation dynamics of Li+ ions. Herein, we propose a wide-temperature LCILEs with 1,3-dichloropropane (DCP13) diluent to construct a non-equilibrium solvation structure under external electric field, wherein the DCP13 diluent enters the Li+ ion solvation sheath to enhance Li+ ion transport and suppress oxidative side reactions at high-nickel cathode (LiNi0.9Co0.05Mn0.05O2, NCM90). Consequently, a Li/NCM90 cell utilizing this LCILE achieves a high capacity retention of 94 % after 240 cycles at 4.3 V, also operates stably at high cut-off voltages from 4.4 V to 4.6 V and over a wide temperature range from -20 °C to 60 °C. Additionally, an Ah-level pouch cell with this LCILE simultaneously achieves high-energy-density and stable cycling, manifesting the practical feasibility. This work redefines the role of diluents in LCILEs, providing inspiration for electrolyte design in developing high-energy-density batteries.

Nanostructured Solid Electrolytes for Enhanced Safety and Performance of Battery Materials

Solid-state batteries (SSB) have garnered significant attention by reason of their potential advantages over traditional liquid electrolyte batteries, including higher energy density, enhanced safety, and reduced volume. However, the development and implementation of solid electrolytes confront several challenges, such as lower ionic conductivity, dendrite formation, and interface stability issues. This review explores the current advancements in solid electrolytes (SLs), with a focus on nanostructured materials, including solid polymer electrolytes (SPEs), solid inorganic electrolytes (SIEs), and composite solid electrolytes (CSEs). The review highlights the benefits of nanostructuring in improving mechanical intensity, ionic conductivity and thermostability. Key methods for synthesizing nanostructured solid electrolytes (NSLs), such as the sol-gel method and 3D printing, are discussed. Additionally, the review addresses critical challenges, including the high cost of materials and manufacturing processes, and proposes future research directions to overcome these barriers. The purpose is to comprehensively understand the current status and future potential of NSL in promoting SSB technology.

Poly(ionic) Liquid-Enhanced Ion Dynamics in Cellulose-Derived Gel Polymer Electrolytes.

Gel polymer electrolytes (GPEs) are regarded as a promising alternative to conventional electrolytes, combining the advantages of solid and liquid electrolytes. Leveraging the abundance and eco-friendliness of cellulose-based materials, GPEs were produced using methyl cellulose and incorporating various doping agents, either an ionic liquid (1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [Pyr14][TFSI]), its polymeric ionic liquid analogue (Poly(diallyldimethylammonium bis(trifluoromethylsulfonyl)imide) [PDADMA][TFSI]), or an anionically charged backbone polymeric ionic liquid (lithium poly[(4-styrenesulfonyl)(trifluoromethyl(S-trifluoromethylsulfonylimino) sulfonyl) imide] LiP[STFSI]). The ion dynamics and molecular interactions within the GPEs were thoroughly analyzed using Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Heteronuclear Overhauser Enhancement Spectroscopy (HOESY), and Pulsed-Field Gradient Nuclear Magnetic Resonance Diffusion (PFG-NMR). Li+ transference numbers (tLi+) were successfully calculated. Our study found that by combining slow-diffusing polymeric ionic liquids (PILs) with fast-diffusing lithium salt, we were able to achieve transference numbers comparable to those of liquid electrolytes, especially with the anionic PIL, LiP[STFSI]. This research highlights the influence of the polymer's nature on lithium-ion transport within GPEs. Additionally, micro supercapacitor (MSC) devices assembled with these GPEs exhibited capacitive behavior. These findings suggest that further optimization of GPE composition could significantly improve their performance, thereby positioning them for application in sustainable and efficient energy storage systems.

Electrochemical Characteristics of Ambarella Peel Waste as Liquid Electrolyte for Zn-Cu Biobattery

This study focuses on the electrochemical characterization of Zn-Cu bio-battery cells utilizing electrolytes derived from ambarella peel waste. The primary objectives are to determine the half-cell and full-cell characteristics of these bio-batteries at various concentration ratios and to identify the optimal concentration ratio for maximum performance. Cyclic voltammetry analysis of the half-cells revealed an oxidation peak at 0.5 V vs Ag/AgCl, corresponding to the conversion of uronic acid to aldaric acid. Additionally, two reduction peaks were observed: hydrogen ion reduction to H2 at 0 V vs Ag/AgCl and water reduction at –0.42 V vs Ag/AgCl. The rate-determining step analysis indicated that the redox reactions in the ambarella peel electrolyte solution were surface reactions. The highest rate constant (ks) of 0.722 ± 0.05 s–1 was observed at a 1:2 concentration ratio. This ratio also resulted in the highest battery capacity of 0.0816 mAh and the maximum power density of 16.13 mW/m2. The study concluded that the 1:2 concentration ratio of ambarella peel waste electrolyte solution is optimal, outperforming the 1:1 and 1:3 ratios in terms of battery capacity and power density.

Electrochemical Deterioration of a Gold Thin Film in Bicarbonate Solution: Correlative Optical, Nano-Mechanical, and Chemical Considerations.

The electrochemical dissolution of metals in liquid electrolytes is of great concern for various electrochemical technologies. However, it is also the focus for boosting metal recovery processes, e.g., from electronic wastes, one of which is the extraction of gold (Au) using eco-friendly electrolytes. To shed more light on the possibility and improvement of such metal leaching, this work presents the investigation of electrochemical deterioration of a Au nanofilm coated on a silicon (Si) support─ubiquitous materials in electronic components─in aqueous potassium bicarbonate (KHCO3) electrolyte, a solution widely used in food products. In addition to the time-dependent in situ Raman spectra revealing the reduced reflectivity of Au associated with its molecular degradation, the significant role of the electric double layer (EDL) at the metal/electrolyte interface is also indicated. Analyzing surface adhesion maps and force-distance spectra acquired using atomic force microscopy and spectroscopy (AFM/AFS), metal degradation is related to nanoscale worm-shaped reconstructed surface features that act as local sites of reduced refractive index. Complemented by the non-negligible fraction of K observed on the treated Au surfaces using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), an electrochemical framework of metal degradation is proposed, depicting the electric-field-induced transport of K+ and H+ ions toward the Au surface regardless of bias polarity and implying the formation of ternary gold hydrides. The consideration of faradic current in the EDL circuit also suggests the occurrence of ternary gold oxides. Such determination is reinforced by the attributability of the polar and electrostatic characteristics of the worm-like features to residual negatively charged anionic clusters of the hydrides and the oxides. The analysis process and the new understanding of metal degradation provide a potential route for inspecting other metal/solution systems.

I3‐‐Mediated Oxygen Evolution Activities to Boost Rechargeable Zinc‐Air Battery Performance with Low Charging Voltage and Long Cycling Life

An effective strategy to facilitate oxygen redox chemistry in metal‐air batteries is to introduce a redox mediator into the liquid electrolyte. The rational utilization of redox mediators to accelerate the charging kinetics while ensuring the long lifetime of alkaline Zn‐air batteries is challenging. Here, we apply commercial acetylene black catalysts to achieve an I3‐‐mediated Zn‐air battery by using ZnI2 additives that provide I3‐ to accelerate the cathodic redox chemistry and regulate the uniform deposition of Zn2+ on the anode. The Zn‐air battery performs an ultra‐long cycle life of over 600 h at 5 mA cm‐2 with a final charge voltage of 1.87 V. We demonstrate that I‐ mainly generates I3‐ on the surface of carbon catalysts during the electrochemically charging process, which can further chemically react with OH‐ to generate oxygen and further revert to I‐, thus obtaining a stable electrochemical system. This work offers a strategy to simultaneously improve the cycling life and reduce the charging voltage of Zn‐air batteries through redox mediator methods.

I3--Mediated Oxygen Evolution Activities to Boost Rechargeable Zinc-Air Battery Performance with Low Charging Voltage and Long Cycling Life.

An effective strategy to facilitate oxygen redox chemistry in metal-air batteries is to introduce a redox mediator into the liquid electrolyte. The rational utilization of redox mediators to accelerate the charging kinetics while ensuring the long lifetime of alkaline Zn-air batteries is challenging. Here, we apply commercial acetylene black catalysts to achieve an I3--mediated Zn-air battery by using ZnI2 additives that provide I3- to accelerate the cathodic redox chemistry and regulate the uniform deposition of Zn2+ on the anode. The Zn-air battery performs an ultra-long cycle life of over 600 h at 5 mA cm-2 with a final charge voltage of 1.87 V. We demonstrate that I- mainly generates I3- on the surface of carbon catalysts during the electrochemically charging process, which can further chemically react with OH- to generate oxygen and further revert to I-, thus obtaining a stable electrochemical system. This work offers a strategy to simultaneously improve the cycling life and reduce the charging voltage of Zn-air batteries through redox mediator methods.

Exfoliating Ti3AlC2 MAX into Ti3C2Tz MXene: A Powerful Strategy to Enhance High‐Voltage Dielectric Performance of Percolation‐Based PVDF Nanodielectrics

AbstractAll‐solid‐state polymer dielectrics benefit from a superior voltage window and conveniently circumvent fire hazards associated with liquid electrolytes. Nevertheless, their future competitiveness with alternative energy storage technologies requires a significant enhancement in their energy density. The addition of conductive 2D MXene particles is a promising strategy for creating percolation‐based nanodielectrics with improved dielectric response. However, a full understanding of the nanodielectric production – microstructure – dielectric performance correlations is crucial. Therefore, this research considered Ti3AlC2 MAX phase and Ti3C2Tz MXene as electrically conductive ceramic fillers in polyvinylidene fluoride (PVDF). Microstructural characterization of both nanodielectrics demonstrated excellent filler dispersion. Additionally, the exfoliation of Ti3AlC2 brought forth extensive alignment and interface accessibility, synergistically activating a pronounced interfacial polarization and nanocapacitor mechanism that enhanced the energy density of PVDF by a factor 100 to 3.1 Wh kg−1@0.1 Hz at 22.9 vol% MXene filler. The stellar increase in the PVDF energy density occurred for a broad MXene filler loading range owing to the unique 2D morphology of MXenes, whereas the addition of Ti3AlC2 fillers only caused a detrimental reduction. Hence, this study buttressed the importance to exfoliate the parental MAX phase into multi‐layered MXene as a decisive strategy for boosting nanodielectric performance.

Polymer electrolytes based on PEO and lithium tetraalkoxyborate salts with ionic liquid properties for lithium-based batteries

The development of lithium-ion batteries (LIBs) with improved safety features is crucial due to the inherent risks associated with liquid electrolytes, such as fires, explosions, and leakage. This study explores the potential of solid polymer electrolytes (SPEs) based on poly(ethylene oxide) (PEO) and lithium tetraalkoxyborate salts (LiTAB) with ionic liquid properties as a safer alternative. Ionic liquids (ILs) are examined for their high ionic conductivity, wide electrochemical window, and excellent thermal stability, despite their high synthesis costs and viscosity challenges. The study proposes the use of a novel LiTAB salt with an oligomeric star-shaped anion structure that reduces mobility, enhancing lithium ion transference numbers. This IL serves as both a lithium salt and an active plasticizer in PEO-based SPEs, offering potential for 3D printing applications. Experimental results demonstrate that these electrolytes exhibit favorable rheological properties, high ionic conductivities, and significant lithium ion transference numbers, addressing the key limitations of conventional PEO-based electrolytes. The findings suggest that incorporating these LiTAB salts in SPEs could significantly enhance the safety and performance of LIBs, particularly for applications in miniaturized consumer electronics and electronic implants.

Pectin alignment induced changes in ion solvation structure in ethylene carbonate-based liquid electrolytes

Classical molecular dynamics simulations are used to explore the impact of the alignment of pectin over the randomized configuration on ion solvation structure in pectin-loaded ethylene carbonate - lithium bis (trifluoromethanesulfonyl) imide electrolytes. Our study focuses on how biological macromolecules, specifically pectin, influence the behavior of liquid electrolytes, considering their applications in rechargeable batteries due to their ion solvation capabilities and ion transport characteristics. Aligned pectin causes a tightly packed first coordination shell of anions around lithium ions by weakening the long-ranged interactions beyond the first coordination shell compared to a random configuration. Consequently, the number of pectin oxygens around lithium decreases dramatically from 3 to 2, resulting in an overall diluted solvation shell containing fewer numbers of anions and pectin oxygens around lithium ions. With polymer alignment, the non-Gaussianity increases from 3.387 to 6.550 for lithium ions and from 0.475 to 0.621 for TFSI ions, reflecting a 90 % increase in dynamic heterogeneity for lithium ions and a 30 % increase for TFSI ions. Cation-cation correlations enhance ionic conductivity in randomized pectin, whereas isolated anion motion dominates in aligned pectin due to cation-pectin interactions. Our work not only highlights potential strategies for improving electrolyte performance in rechargeable batteries but also emphasizes the crucial role of molecular orientation in optimizing electrolyte properties, paving the way for more optimized and efficient battery technologies.

Robust polymer electrolytes with fast ion-transport nanochannels constructed by carbon dots for long lifespan Li metal batteries

As an anode material in energy storage systems, Li metal has exceptional merits, including high specific capacity, low density, and low redox potential. However, challenges such as lithium dendrites and unstable solid electrolyte interphase (SEI) hinder the practical application of lithium metal batteries (LMBs). Solid polymer electrolytes (SPEs), notably PVDF-HFP, are expected to overcome the above problems because of their mechanical merits and safe features, but their limited ion transportation behaviors result in insufficient ionic conductivity at room temperature. Herein, we invent an approach to prepare high performance electrolytes composed by porous PVDF-HFP and functionalized carbon dots (CDs). Such porous PVDF-HFP polymer membranes are created by a subtle phase inversion process, possessing a sponge-like structure, vertical lithium-ion transport channels and CDs decorated surfaces, thus able to uptake the liquid electrolyte (LE) to form gel polymer electrolytes (GPEs). The CDs fillers are produced in large scale with adjustable surface states, which can enhance Li salts disassociation to release free Li ions. As a result, the optimal conductivity of the as-prepared GPEs at room temperature is up to 8.7 mS cm−1 and the lithium transference number reaches 0.64. Our GPEs endow Li symmetric batteries with very stable SEI and long cycling life over 2200 h, and help realize high capacities and retention rates of the LMBs using LiFePO4(LFP) or LiCoO2(LCO) cathodes.

Bioinspired Design of Vascularized Glassy Metal-Organic Frameworks Electrolyte for Quasi-Solid-State Sodium Batteries

Quasi-solid-state electrolytes (QSSEs) are regarded as the most promising alternative for next-generation battery technology due to the compatibility of assemble process and high safety. However, the rational design of solid hosts to ensure the high-efficiency utilization of tiny liquid electrolytes and the deep understanding of ion transport mechanisms at heterogeneous structures are still challenging. Herein, inspired by the ion transport in biological blood vessels, we propose a nitrogen vacancy modified glassy metal-organic framework (MOF) as Na-ion QSSEs host, which shows multilevel ions transport channels, isotropy property, and no grain boundaries. The vascularized glassy MOF enables the reasonable distribution of a small amount of solvent (14 wt.% (solvent as a percentage of QSSE by mass)) in both macro and microenvironments with specific functions, boosting the fast Na-ion transport (1.18 × 10−4 S cm–1, 30°C) and Na-ion transfer number (0.92), and homogeneous Na-ion nucleation/propagation even at -50°C. Meanwhile, the quasi-solid-state Na||Na3V2(PO4)3/C cell demonstrates excellent rate capability and long cycling stability (0.0288% capacity decay per cycle after 500 cycles). The bioinspired design of glassy MOF will shed light on new avenues for the development of energy storage and conversion.

Role of Anion Flexibility on Graphite Electrode Reactions in Bis(fluorosulfonyl)amide-Based Ionic Liquid Electrolytes for Lithium-Ion Batteries

Role of Anion Flexibility on Graphite Electrode Reactions in Bis(fluorosulfonyl)amide-Based Ionic Liquid Electrolytes for Lithium-Ion Batteries

Tracking the Early-life of PtNi/C Shape-Controlled Catalysts upon their Integration in PEMFC

Abstract The integration of promising bimetallic electrocatalytic active materials for oxygen reduction reaction (ORR) into practical and functional proton-exchange membrane fuel cell (PEMFC) electrodes remains largely impeded by the poor performances that these exhibit at high current loads. The early life of PtNi/C catalysts presenting either structurally faceted/ordered or defective/disordered surface morphology is compared to that of both spherical PtNi/C and Pt/C catalysts. Different single-cell operating conditions were studied. At low current density, in the kinetically limited region, a good agreement between liquid electrolyte and single-cell configuration is reported and the kinetic benefit of PtNi/C catalysts compared to Pt/C is (at least partially) maintained. However, PtNi/C catalysts show severe limitations in the O2 mass transport limited region. Morphological and compositional changes were monitored at each stage showing that Ni atoms are leached at every step from ink formulation to the first PEMFC test. We show that Ni is already redistributed in the membrane in the fresh membrane electrode assembly (MEA) state. Ni2+ cationic contamination of the ionomer/membrane contributes to the disappointing results obtained in MEA configuration. In addition, for shaped-controlled PtNi/C, the surface faceting loss combined with restructuring via coalescence and crystallite growth further compromise their transfer in technological devices.

A facile one-pot synthesis of hierarchical porous carbon for supercapacitor electrodes

This study presents a facile, environmentally friendly approach to fabricate hierarchical porous carbon for supercapacitor electrodes. The one-pot synthesis of PFO/silica/PTFE via co-pyrolysis generates ideal hierarchical porous carbon. Compared with traditional methods, this method eliminates toxic solvents and complex cleaning steps. PPC-2 obtained under the optimized activation time has the highest specific surface area (2657 m2 g−1) and a remarkable total pore volume (2.96 cm3 g−1). These properties result in a remarkable specific capacitance of 335.9–210.8 F g−1 at current densities of 0.5–10 A g−1 in KOH electrolyte. The electrochemical performance of the PPC-2 electrode in a symmetric supercapacitor device was measured in aqueous (6 M KOH) and ionic liquid (EMIM-TFSI) electrolytes. In EMIM-TFSI, PPC-2//PPC-2 provides an energy density of 48.5 Wh/kg even at a power density of 750 W kg−1. This facile one-pot synthesis method offers a sustainable and scalable approach to produce high-performance hierarchical porous carbon for supercapacitor applications.

Mechanistic Understanding of Long Duration Fast Charge Aqueous Zinc Batteries Using Physically Adsorbed Oligomers as Interphases.

Polymers have been used as additives in the liquid electrolytes typically used for secondary batteries that utilize metals as anode. Such additives are conventionally argued to improve long-term anode performance by suppressing morphological and hydrodynamic instabilities thought to be responsible for out-of-plane and dendritic metal deposition during battery charging. More recent studies have reported that the polymer additives provide even more fundamental mechanisms for stabilizing metal electrodeposition through their ability to regulate metal electrodeposit crystallography and, thereby, morphology. Few studies explore how polymers carried in a liquid electrolyte achieve these functions, and fewer still provide rules for choosing among the various polymer types, the additive polymer molecular weight (Mw), and concentration in the electrolyte. Here, we investigate how these generally easy-to-control variables influence electrochemical interphase formation inside battery cells and their impact on the morphology and reversibility of Zn electrodes in aqueous electrolytes. We focus on aqueous Zn-iodine electrochemical cells containing linear polyethylene glycol (PEG) chains as additives and find that in electrolytes where the polymer concentration is maintained in the dilute solution regime there is an optimum polymer molecular weight (Mw ≈ 1000 Da), above which beneficial effects of polymers on Zn electrode reversibility and Zn-I2 battery lifetime are progressively lost. By means of optical ellipsometry and theoretical calculations, we show that the optimal Mw is associated with saturation of the thickness of a physiosorbed PEG coating on the Zn metal electrode. Electron microscopy and X-ray photoelectron spectroscopy analysis of Zn electrodeposits formed in such electrolytes reveal that the physiosorbed polymer coating has two primary effects─it regulates the deposit morphology and suppresses parasitic reactions between the electrode and electrolyte components. The parasitic reactions produce species like ZnO, which are known to passivate the Zn electrode and promote nonuniform deposition. Galvanostatic cycling measurements in aqueous Zn-I2 cells containing the PEG additives at the optimal Mw show that the cells maintain very high Coulombic efficiencies (≥99%) at current densities as high as 50 mA/cm2─close to the maximum values permissible across the Celgard separator membranes used in our studies.