Anode-electrolyte Interface Research Articles

Regulating the Interfacial Charge Density by Constructing a Novel Zn Anode-Electrolyte Interface for Highly Reversible Zn Anode.

Aqueous zinc-ion batteries (AZIBs) have attracted considerable attention. However, due to the uneven distribution of charge density at Zn anode-electrolyte interface, severe dendrites and corrosion are generated during cycling. In this work, a facile and scalable strategy to address the above-mentioned issues has been proposed through regulating the charge density at Zn anode-electrolyte interface. As a proof of concept, amidinothiourea (ATU) with abundant lone-pair electrons is employed as an interfacial charge modifier for Zn anode-electrolyte interface. The uniform and increased interfacial charge distribution on Zn anode-electrolyte interface has been obtained. Moreover, the unique Zn-bond constructed between N atoms and Zn2+ as well as the hydrogen bonds are formed among ATU and Ac- anion/active H2 O, which promote the migration and desolvation behavior of Zn2+ at anode-electrolyte interface. Accordingly, at a trace concentration of 0.01 mg mL-1 ATU, these features endow Zn anode with a long cycling life (more than 800 h), and a high average Columbic efficiency (99.52 %) for Zn||Cu batteries. When pairing with I2 cathode, the improved cycling ability (5000 cycles) with capacity retention of 77.9 % is achieved. The fundamental understanding on the regulation of charge density at anode-electrolyte interface can facilitate the development of AZIBs.

Ionic-cellulose-adhesive modulated aqueous electrolyte enables water-poor and stable anion-derived electrolyte interphase for durable and dendrite-free zinc metal batteries

The development of aqueous zinc-ion batteries (ZIBs) as attractive candidates is largely limited by the unstable anode/electrolyte interface (AEI), which causes dendrite formation and by-products. Here, an inexpensive ionic cellulose adhesive, carboxymethylcellulose sodium (CMC), is utilized as an interface stabilizer to controllably manipulate the AEI for reversible Zn plating/stripping behaviors. The CMC derived anions have a propensity to initially gather on the Zn surface, forming a unique H2O-poor and CMC--rich electrical double layer (EDL) for relieving the water-induced side reactions and promoting fast Zn2+ transport kinetics. Meanwhile, an adaptive solid electrolyte interphase (SEI) can be triggered during cycling to further tune interfacial Zn2+ deposition behaviors. Such a combination enables exposure of (002) facets with dendrite-free and compact Zn deposition on Zn metal. Accordingly, the Zn//Zn symmetric cells with CMC-based electrolyte achieve outstanding lifespan with a 26-fold enhancement for 3125 h at 1 mA cm−2 and 1 mA h cm−2. Also, the Zn anode is promoted to run over 4000 cycles with high Zn reversibility of 99.7%. When paired with NaV3O8·1.5 H2O (NVO) cathode, the full cell with CMC achieves a prominent stability for 2500 cycles at 3 A g−1, much better than that in pure ZnSO4 electrolyte.

Operando Electrochemical Liquid Cell Scanning Transmission Electron Microscopy Investigation of the Growth and Evolution of the Mosaic Solid Electrolyte Interphase for Lithium-Ion Batteries.

The solid electrolyte interphase (SEI) is a key component of a lithium-ion battery forming during the first few dischage/charge cycles at the interface between the anode and the electrolyte. The SEI passivates the anode-electrolyte interface by inhibiting further electrolyte decomposition, extending the battery's cycle life. Insights into SEI growth and evolution in terms of structure and composition remain difficult to access. To unravel the formation of the SEI layer during the first cycles, operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) is employed to monitor in real time the nanoscale processes that occur at the anode-electrolyte interface in their native electrolyte environment. The results show that the formation of the SEI layer is not a one-step process but comprises multiple steps. The growth of the SEI is initiated at low potential during the first charge by decomposition of the electrolyte leading to the nucleation of inorganic nanoparticles. Thereafter, the growth continues during subsequent cycles by forming an island-like layer. Eventually, a dense layer is formed with a mosaic structure composed of larger inorganic patches embedded in a matrix of organic compounds. While the mosaic model for the structure of the SEI is generally accepted, our observations document in detail how the complex structure of the SEI is built up during discharge/charge cycling.

Heterocyclic polymer supported cathode/Li interface layers to lower the operational temperature of PEO-based Li-batteries

High-performance poly (ethylene oxide) (PEO)-based solid-state polymer Li-batteries (SSLBs) at low temperature (≤ 25 ℃) is hindered by high interfacial resistance and low ionic conductivity. Herein, we simultaneously construct cathode and anode interface layers via in-situ heat-induced heterocyclic polymerization reaction, where the cathode-electrolyte interface layer (PPL) consists of bromine-doped poly (3,4-ethylene-dioxy-thiophene) (PEDOT), PEO and bis-trifluoromethanesulfonimide (LiTFSI), featuring with mixed ionic/electronic conduction, and the anode-electrolyte interface layer (PVCL) was formed by poly (vinyl carbonate) (PVC), PEO and LiTFSI, having a robust fast ionic conduction. Benefiting from the PEDOT conductivity, high mechanical strength of PVC and good interface affinity aroused by heat-induced reaction, the solid-state PEO-based LiFePO4||Li cell shows low interfacial resistance of 11.02 Ω that decreased by 92% compared to the cell without interface modification, and delivering a discharge capacity of 164.4 mAh g−1 at 0.1 C (25 ℃), as high as 115.9 mAh g−1 at 10 ℃. X-ray photoelectron spectroscopy revealed the enrichment of LiF, Li3N and LiBr on the lithium metal surface after cycling, further enhancing stable cycling Li-batteries. The dual interface-constructed strategy provides a reliable way to resolve the bottle-neck interfacial issues of SSLBs.

Microstructural Changes in Ni-YSZ Electrodes Operated in Fuel Cell and Electrolysis Modes: Effect of Gas Diffusion Limitations

Lifetime performance stability is a key issue for the commercialization of solid oxide cells. Ni migration in Ni-YSZ electrode supported cells is an important degradation mechanism. Here we present the results of life tests on symmetric Ni-YSZ electrode-supported cells. These symmetric cells have similar processing and microstructure as conventional Ni-YSZ-supported cells, but the symmetric structure provides information on the Ni-YSZ electrode operating as both an anode and a cathode in the same test. Life tests of up to 1000 h were carried out at 800 ˚C in 50-50 H2-H2O at current densities of 0, 0.75, 1.00, and 1.50 A/cm2. Total applied voltage to each cell was tracked over the lifetime, and small portions of the cells were removed during the life tests to study the time-dependent changes in microstructure.Figure 1 summarizes the microstructural results from a Ni-YSZ cell operated at 1.0 A/cm2, observed at 100, 500, and 1000 h. 2D and 3D microstructure characterization was used to show the volume fractions of pore and active (electrically connected) Ni versus position. Somewhat surprisingly, the cathode microstructure remains relatively unchanged compared to a non-polarized cell, with no evidence of Ni migration or isolation. In contrast, Ni migration and isolation was observed to increase with time at the anode in polarized cells, with the thickness of the Ni deactivated region growing from ~5 mm at 500 h to ~15 mm at 1000 h for 1.0 A/cm2 and ~2 μm at 500 h and ~8 μm at 1000 h for 0.75 A/cm2. In addition, total cleavage at the anode-electrolyte interface occurs at 1.5 A/cm2 by 100 h, and at 1.0 A/cm2 by 1000 hr. The increase of porosity in the altered zones clearly shows where Ni is depleted. There is no evidence of Ni enrichment adjacent to the depleted region, as might be expected if Ni was moving via surface diffusion.Although there have been numerous recent reports of Ni migration/isolation in Ni-YSZ cathodes during electrolysis cell operation1, Ni migration has also been reported in Ni-YSZ fuel cell anodes2,3. Here we suggest that such results can be explained by a relatively high steam content in the Ni-YSZ anode functional layer. Conversely, the lack of Ni migration in the electrolysis cathode can be explained by a relatively low steam content in the cathode functional layer. To quantitatively assess the gas compositions, one-dimensional modeling of the electrochemical and gas diffusion processes of these cells was performed using a finite difference method (FDM) with modified Butler-Volmer kinetics and the dusty-gas model respectively. Using diffusivity values calculated via electrochemical impedance spectroscopy and microstructural measurements, the modeling reveals that electrochemically active Ni sees significantly different gas composition than the inlet, creating steam-rich anodes (PH2O = 0.73, 0.8, and 0.95 atm for 0.75, 1.0 and 1.5 A/cm2 respectively) and steam-depleted cathodes (PH2O = 0.27, 0.2, and 0.05 atm for 0.75, 1.0 and 1.5 A/cm2 respectively). This is in accord with results and models suggesting that Ni migration is important mainly under high steam conditions, probably due to vapor transport. Note that these effects are exacerbated by the relatively low porosity and small pore size in the present electrodes that lead to asymmetric Knudsen diffusion, wherein H2O diffuses at ~1/3 the rate of H2. These results suggest that the nature of the porosity in Ni-YSZ supports can lead to significant variations in the extent and directionality of Ni migration.Figure 1: (a, b, c) Polished cross sectional backscatter electron (BSE) images and (d,e,f) low voltage secondary electron (LV-SE) images of an electrode-supported symmetric Ni-YSZ cell at 100, 500, and 1000 h of galvanostatic operation at 1.00 A/cm2 in 50-50 H2-H2O and T = 800 ˚C. BSE images reveal a depletion of total Ni at the anode-electrolyte interface (AEI) by a net increase in porosity, and eventual cleavage at that line. LV-SE images reveal that near total deactivation of Ni occurs near the AEI as well. (g,h,i) Quantitative image analysis reveals the extent of porosity increase (via Ni depletion) and Ni deactivation at 100, 500, and 1000 hours. The regimes for both events exactly overlap, with the depletion/deactivation extending 0, 5, and 15 μm from the AEI, respectively. M. B. Mogensen et al., Fuel Cells, 21, 415–429 (2021).J. Geng et al., J. Power Sources, 495, 229792 (2021).Z. Jiao and N. Shikazono, J. Power Sources, 396, 119–123 (2018). Figure 1

Interface Controls Large-Volume Change Anodes Pulverization

Micron sized alloys have been considered as the most attractive candidates for advanced lithium or sodium ion battery anodes due to their high capacity, cost effectiveness, and ease of mass production. However, their large volume variation during (de)alloying reaction with Li or Na ions causes severe mechanical degradation of anode materials, resulting in particle pulverization and loss of electrical interparticle contact. In addition, this substantial volumetric fluctuation leads to newly exposed anode surface to electrolyte and instability of solid-electrolyte interphase (SEI), which can bring about continuously formation of SEI layers. To mitigate the large volume change issues of micron sized alloys, various approaches have been studied such as introducing various electrolytes and additives for stabilizing the SEI layers. However, these modified SEI layers are still not enough to suppress the large volume fluctuation of micron sized alloys.Here, we demonstrate that the effect of interface between electrolyte and anode surface on anode pulverization. With micron sized alloying anodes for sodium-ion batteries (Bi and Sn), we observed substantially different pulverization behavior as a choice of electrolyte solvents leading to different anode-electrolyte interface. This different interface reactivity between solvents has a big impact on not only pulverization behavior of alloying anodes but also formation and growth of SEI layers on the surface of anode. Thus, the electrochemical performances of the alloying anodes also can be influenced by its interface characteristics. We thoroughly analyzed the effect of interface of alloying anode from electrode-level to nanoscale by various characterization tools such as Scanning electron microscopy (SEM), X-ray computed tomography (X-ray CT), X-ray photoelectron spectroscopy (XPS), Atom probe tomography (APT), and cryo-transmission electron microscopy (TEM). Moreover, we clarified the mechanism of the interface reaction and pulverization pathway by theoretical simulations. We believe this study can help researchers to understand the degradation behavior of large volume change alloy anodes.

Synergistic "Anchor-Capture" Enabled by Amino and Carboxyl for Constructing Robust Interface of Zn Anode.

While the rechargeable aqueous zinc-ion batteries (AZIBs) have been recognized as one of the most viable batteries for scale-up application, the instability on Zn anode-electrolyte interface bottleneck the further development dramatically. Herein, we utilize the amino acid glycine (Gly) as an electrolyte additive to stabilize the Zn anode-electrolyte interface. The unique interfacial chemistry is facilitated by the synergistic "anchor-capture" effect of polar groups in Gly molecule, manifested by simultaneously coupling the amino to anchor on the surface of Zn anode and the carboxyl to capture Zn2+ in the local region. As such, this robust anode-electrolyte interface inhibits the disordered migration of Zn2+, and effectively suppresses both side reactions and dendrite growth. The reversibility of Zn anode achieves a significant improvement with an average Coulombic efficiency of 99.22% at 1mAcm-2 and 0.5mAhcm-2 over 500 cycles. Even at a high Zn utilization rate (depth of discharge, DODZn) of 68%, a steady cycle life up to 200h is obtained for ultrathin Zn foils (20μm). The superior rate capability and long-term cycle stability of Zn-MnO2 full cells further prove the effectiveness of Gly in stabilizing Zn anode. This work sheds light on additive designing from the specific roles of polar groups for AZIBs.

Operando Characterization of Plating and Stripping Dynamics of Li-Mg Alloy Anode and Sulfide Solid Electrolyte Interface

All-solid-state lithium metal batteries are projected to offer one of the highest specific energy among rechargeable batteries, positioning them as a front-runner for electric vehicle applications. Lithium metal anodes outperform conventional graphite anodes in terms of cell-level energy density. However, maintaining a conformal metal–electrolyte contact is a great challenge. The volumetric change of the lithium metal anode during stripping produces voids, which deteriorates the Li–electrolyte contact. To address this challenge, β-phase Li solid solution (i.e., Li-Mg alloy) has been shown to exhibit improved contact with the solid electrolyte during stripping. Moreover, Li solid solution has a similar electrochemical potential as Li, making it a potential replacement for Li metal anodes without sacrificing cell-level energy density. In this study, we show that the chemical properties of the alloy play an essential role in the morphological stability of metal–solid electrolyte interface. We compare the stripping behavior of pure Li and Li-Mg alloy anodes in argyrodite electrolyte and characterize the morphological evolution of the interface using operando scanning electron microscopy (SEM). We also analyze the electro-chemo-mechanical properties of Li and Li alloy anodes during stripping with galvanostatic electrochemical impedance spectroscopy (GEIS) to compare the influence of composition change and interfacial void on the electrode overpotential and interface resistance. Our research visualizes the morphological and compositional evolution of alloy metal anode during stripping and rationalizes their improved interfacial stability against solid electrolytes.Acknowledgment: This work was supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Vehicle Technologies Program under Contract DE-EE0008864. Figure 1

Stabilizing Zinc Anodes by a Uniform Nucleation Process with Cysteine Additive.

Zinc anodes in aqueous batteries face challenges such as dendrite growth and interfacial instability. This study investigates the use of cysteine as an electrolyte additive to address these issues. By establishing the correlation between the size of zinc nuclei and the surface tensions/contact angle at the electrolyte-anode interface, it is demonstrated that the addition of cysteine in the electrolyte alters the surface tensions/contact angle at the electrolyte-anode interface and the nucleation process of zinc. This alteration results in the formation of smaller and more dispersed nuclei, as opposed to the formation of larger island grains. This has a profound impact on the subsequent deposition growth process, enabling smooth and uniform zinc electrodeposition without the formation of dendrites. Additionally, cysteine molecules create a stable interface during zinc plating and stripping, effectively preventing corrosion from side reactions. The incorporation of cysteine in the electrolyte significantly enhances cycling stability and extends the lifespan of zinc anodes in aqueous batteries.

Hemimorphite /C interface layer with dual-effect methodically redistricted Zn2+ deposition behavior for dendrite-free zinc metal anodes

The uneven distribution of Zn2+ gradient and electric fields at the electrolyte–anode interface are the two “pain points” that seriously limit the lifespan of AZIBs. Traditional artificial SEI layers targeted one single “pain points” cannot simultaneously balance the Zn2+ gradient and electric fields. Herein, hemimorphite/C interface layer, sandwich structure Zn4(Si2O7)(OH)2·H2O@rGO@Zn4(Si2O7)(OH)2·H2O (rGO@ZnSi) prepared by in-situ growth strategy is provided as “dual-effect” to modulate Zn2+ gradient and electric fields regulation. The rGO@ZnSi is demonstrated with the zincophilicity due to Zn-ion-conducive transport channel about 5Å and boosted electroconductibility properties by in situ growth rGO. The internal rGO acts as conductive core, facilitating the rapid transfer of electrons along the two-dimensional plane, thus significantly enhancing the conductivity of hemimorphite. Additionally, it opens up a new territory for Zn2+ reduction process, which would enhance the reversibility of Zn anode, mitigate the polarization and promote electrochemical performance. The Zn//Zn battery with the modified rGO@ZnSi SEI exhibits an ultra-long and outstanding cycling stability of up to 170 days. Benefitting from the rGO@ZnSi SEI, the rGO@ZnSi-Zn//V2O5 full battery delivers a high discharge capacity and long cycle performance. The “dual-effect” rGO@ZnSi SEI escorts for the dendrite-free zinc metal anodes with lifetime extension, ultra-high rate performance and cost-effectiveness.

Ice-Template-Induced Highly Interconnected Porous Polymer Gel Electrolytes for Dendrite-Free Flexible Zinc-Air Batteries.

Improving the performance of quasi-solid-state gel polymer electrolytes is critical for addressing issues at the Zn anode-electrolyte interface of high-performance flexible Zn-air batteries (FZABs). In this study, a highly interconnected porous poly(vinyl alcohol)/poly(ethylene glycol) (PVA/PEG) hydrogel electrolyte was fabricated via an ice-crystal template for FZABs. The mechanical toughness and stability of the gel electrolytes can be reinforced by the formation of a PEG-PVA cross-linking network. The three-dimensional PVA/PEG porous skeleton greatly increased electrolyte uptake and accelerated ion transport, leading to high ionic conductivity (42.5 mS cm-1). In-situ synchrotron radiation X-ray imaging revealed that the PVA/PEG network can effectively inhibit dendrite growth and the hydrogen evolution reaction. The assembled FZABs exhibited superior cycle stability, high power density (109 mW cm-3), and excellent flexibility and structural stability under bending conditions, thus showing great potential for future applications in flexible and wearable electronic device technologies.

Critical triple roles of sodium iodide in tailoring the solventized structure, anode-electrolyte interface and crystal plane growth to achieve highly reversible zinc anodes for aqueous zinc-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) are promising for energy storage. However, the Zn dendrite and corrosive reactions on the surface of Zn anode limit the practical uses of ARZIBs. Herein, we present a valid electrolyte additive of NaI, in which I- can modulate the morphology of Zn crystal growth by adsorbing on specific crystal surfaces (002), and guide Zn deposition by inducing a negative charge on the Zn anode. Simultaneously, it enhances the reduction stability of water molecules by participating in the solvation structure of Zn(H2O)62+ by forming ZnI(H2O)5+. At 10 mA cm−2, the assembled Zn symmetrical batteries can run stably over 1,100 h, and the depth of discharge (DOD) can reach 51.3 %. At 1 A g−1, the VO2||Zn full-cell in 2 M ZnCl2 electrolyte with 0.4 M NaI (2 M ZnCl2-0.4 M NaI) maintains of the capacity retention of 75.7 % over 300 cycles. This work offers an insight into inorganic anions as electrolyte additives for achieving stable zinc anodes of ARZIBs.

Unraveling the Solvation Structure and Electrolyte Interface through Carbonyl Chemistry for Durable and Dendrite‐Free Zn Anode

AbstractAqueous Zn ion batteries are appealing systems owing to their safety, low cost, and environmental friendliness; however, their practical applicability is impeded by the growth of Zn dendrites and side reactions. Herein, a dual‐functional electrolyte additive, namely acetylacetone (AT) is utilized for the simultaneous regulation of the solventized structure and anode–electrolyte interface (AEI) to achieve a durable, dendrite‐free Zn anode. Theoretical calculations and experimental characterizations reveal that the AT molecule can be adsorbed onto Zn metal surface to reconstruct the AEI and allow for the primordial desolvation of [Zn(H2O)6]2+ at locations away from the surface of the Zn anode during deposition, which is attributed to the strong polarity of the carbonyl functional group. In addition, the two carbonyls of AT can replace two H2O molecules in the primary solventized structure of Zn2+ to reduce the number of active H2O molecules, efficiently suppressing Zn dendrite growth and detrimental reactions. As a proof of concept, a Zn//Cu cell is constructed in ZnSO4 containing 3 vol.% AT electrolyte, delivering stable cycling over 1800 cycles while maintaining a high Coulombic efficiency of 99.74%. This study provides a practical approach for inhibiting dendrite growth and side reactions by harnessing carbonyl chemistry.

An Overview on Transport Phenomena within Solid Electrolyte Interphase and Their Impact on the Performance and Durability of Lithium-Ion Batteries

The nature of the electrode–electrolyte interface has an impact on the performance and durability of lithium-ion batteries (LIBs). The initial electrolyte’s thermodynamic instability at the anode–electrolyte interface in LIBs results in the formation of a passivation layer, called solid electrolyte interphase (SEI). The initial dense and intact layer allows Li+ transport and restricts electron tunneling, thus preventing electrolyte decomposition and ensuring the electrochemical stability of a battery. However, the growth of this layer can reduce the availability of active lithium and electrolyte, and ultimately lead to an irreversible battery capacity fade. Investigating the transport phenomena of lithium ions within SEI is crucial for understanding its formation and growth. Nonetheless, accurately describing all relevant mechanisms is challenging due to its complex and multiscale nature. An overview of current computational efforts to study Li+ transport within SEI is given in this article, ranging from electronic/atomistic scale simulations to macroscopic models. The drawbacks and advantages of the proposed numerical approaches are summarized along with the obstacles that need to be overcome to obtain accurate experimental data, identified on the basis of the most recent literature evidence. We highlight collaboration gaps between modeling and experimental approaches, as well as the urgent need for new multiscale models, to gain a better understanding of such a crucial transport phenomenon.

Synergistic dual electrolyte additives for fluoride rich solid-electrolyte interface on Li metal anode surface: Mechanistic understanding of electrolyte decomposition

Improving the quality of the solid-electrolyte interphase (SEI) layer is highly imperative to stabilize the Li-metal anodes for the practical application of high-energy–density batteries. However, controllably managing the formation of robust SEI layers on the anode is challenging in state-of-the-art electrolytes. Herein, we discuss the role of dual additives fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2, LiPF) within the commercial electrolyte mixture (LiPF6/EC/DEC) considering their reactivity with Li metal anodes using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Synergistic effects of dual additives on SEI formation mechanisms are explored systematically by invoking different electrolyte mixtures including pure electrolyte (LP47), mono-additive (LP47/FEC and LP47/LiPF), and dual additives (LP47/FEC/LiPF). The present work suggests that the addition of dual additives accelerates the reduction of salt and additives while increasing the formation of a LiF-rich SEI layer. In addition, calculated atomic charges are applied to predict the representative F1s X-ray photoelectron (XPS) signal, and our results agree well with the experimentally identified SEI components. The nature of carbon and oxygen-containing groups resulting from the electrolyte decompositions at the anode surface is also analyzed. We find that the presence of dual additives inhibits undesirable solvent degradation in the respective mixtures, which effectively restricts the hazardous side products at the electrolyte-anode interface and improves SEI layer quality.

Temperature‐controlled microextrusion printing for mesoscale interfacial designing in solid oxide fuel cells

AbstractA temperature‐controlled microextrusion printing technique is proposed to realize the increased aspect ratio of mesoscale convex structures at the anode–electrolyte interface in solid oxide fuel cells (SOFCs). The rheological properties of the anode ink for microextrusion printing are experimentally measured at various temperatures, and it is found that the viscosity of the ink and the wettability of the ink to the anode substrate decrease at lower temperatures, which is desirable for the ink to retain its shape on the substrate. The anode‐supported SOFC button cells are fabricated by microextrusion printing with and without temperature control and compared in terms of their interfacial structures and electrochemical performance. The aspect ratio of the interfacial structure is increased from 0.16 to 0.28 by lowering the ink temperature, resulting in a higher interface enlargement of 25%. Owing to the enlarged interfacial area, enhanced cell performance is also achieved.

Microstructural Changes in Ni-YSZ Electrodes Operated in Fuel Cell and Electrolysis Modes: Effect of Gas Diffusion Limitations

Ni-YSZ electrode support symmetric cells were operated at 0, 0.75, 1.00, and 1.50 A/cm2 for 1000 h in 50% H2-50% H2O at 800 ˚C. Electrochemical fracture at the anode-electrolyte interface is observed to occur under high anodic overpotential. Ni migration is observed and quantified over time at the anode of the polarized cells; however, the cathode shows no migration compared to control. Gas diffusion calculations show that steam is significantly enriched and depleted at the anode and cathode respectively, leading to the formation or suppression of volatile Ni(OH)x species, which have been hypothesized as a transport pathway for Ni. However; gas flux calculations show that chemical evaporation alone is unlikely to be fast enough to induce the Ni loss observed.

Designing Solvated Double-Layer Polymer Electrolytes with Molecular Interactions Mediated Stable Interfaces for Sodium Ion Batteries.

Unstable cathode-electrolyte and/or anode-electrolyte interface in polymer-based sodium-ion batteries (SIBs) will deteriorate their cycle performance. Herein, a unique solvated double-layer quasi-solid polymer electrolyte (SDL-QSPE) with high Na+ ion conductivity is designed to simultaneously improve stability on both cathode and anode sides. Different functional fillers are solvated with plasticizers to improve Na+ conductivity and thermal stability. The SDL-QSPE is laminated by cathode- and anode-facing polymer electrolyte to meet the independent interfacial requirements of the two electrodes. The interfacial evolution is elucidated by theoretical calculations and 3D X-ray microtomography analysis. The Na0.67 Mn2/3 Ni1/3 O2 |SDL-QSPE|Na batteries exhibit 80.4 mAh g-1 after 400 cycles at 1 C with the Coulombic efficiency close to 100 %, which significantly outperforms those batteries using the monolayer-structured QSPE.

A Passivation-Free Solid Electrolyte Interface Regulated by Magnesium Bromide Additive for Highly Reversible Magnesium Batteries.

Highly reversible Mg battery chemistry demands a suitable electrolyte formulation highly compatible with currently available electrodes. In general, conventional electrolytes form a passivation layer on the Mg anode, requiring the use of MgCl2 additives that lead to severe corrosion of cell components and low anodic stability. Herein, for the first time, we conducted a comparative study of a series of Mg halides as potential electrolyte additives in conventional magnesium bis(hexamethyldisilazide)-based electrolytes. A novel electrolyte formulation that includes MgBr2 showed unprecedented performance in magnesium plating/stripping, with an average Coulombic efficiency of 99.26% over 1000 cycles at 0.5 mA/cm2 and 0.5 mAh/cm2. Further analysis revealed the in situ formation of a robust Mg anode-electrolyte interface, which leads to dendrite-free Mg deposition and stable cycling performance in a Mg-Mo6S8 battery over 100 cycles. This study demonstrates the rational formulation of a novel MgBr2-based electrolyte with high anodic stability of 3.1 V for promising future applications.

Unraveling the Interphasial Chemistry for Highly Reversible Aqueous Zn Ion Batteries

A robust solid electrolyte interface (SEI) is crucial to widen the electrochemical stability window of the electrolyte and enable sustainably stable electrode reactions in aqueous Zn ion batteries. Different from the SEI in nonaqueous electrolytes, it is of great importance to form a functional and stable SEI due to parasitic reactions with water in aqueous Zn ion batteries. However, the concrete SEI formation in aqueous electrolytes has been elusive so far. Here, we regulate and unravel the decomposition mechanisms of organic Zn salts at the Zn anode-electrolyte interface in the widely studied zinc triflate-based aqueous electrolytes. By introducing a buffering adsorption layer with an optimal concentration of acetate anions, the uncontrollable decomposition of organic zinc triflate salt is greatly inhibited on Zn anodes, resulting in a stable interface. The average Coulombic efficiency of the Zn anode thus can reach as high as 99.95% and stable cycling for 4200 h. With the cooperation of buffering adsorption layers, the tetraethyl ammonium trifluoromethanesulfonate additive as the decomposition promoter could further regulate the decomposition of triflate anions for the formation of robust SEI layers for Zn anodes in electrolytes with a dilute salt concentration. Zn-polyaniline (PANI) full cells demonstrate stable cycling with controlled N/P ratios in such electrolytes. This work proposes an insightful perspective on rational regulation of the decomposition pathway of electrolyte components by forming a stable electrode-electrolyte interface for improved electrochemical performance of aqueous Zn ion batteries.