Electrolyte Engineering Research Articles

Electrostatic Potential as Solvent Descriptor to Enable Rational Electrolyte Design for Lithium Batteries

AbstractArtificial intelligence/machine learning (AI/ML) applied to battery research is considered to be a powerful tool for accelerating the research cycle. However, the development of appropriate materials descriptors is often the first hurdle toward implementing meaningful and accurate AI/ML. Currently, rational solvent selection remains a significant challenge in electrolyte development and is still based on experiments. The dielectric constant (ε) and donor number (DN) in electrolyte design are insufficient. Finding theoretically computable solvent descriptors for evaluating Li+ solvation is a significant step toward accelerating electrolyte development. Here, based on the electrostatic interaction between Li+ and solvent, the electrostatic potential (ESP) of electrolyte solvent is calculated by density functional theory calculations and reveals significant regularity. ESP as a direct and simple solvent descriptor for conveniently designing electrolytes is proposed. The lowest negative electrostatic potential (ESPmin) ensures the nucleophilic capacity of the solvating solvent and the weak ESPmin means decreased solvation energy. Weak ESPmin and strong highest positive electrostatic potential (ESPmax) are the main characteristics of non‐solvating antisolvents. Using the plot of ESPmin – ESPmax strong solvating solvent, weakly solvating solvent, or antisolvent are identified that have been used in electrolyte engineering. This solvent descriptor can boost AI/ML to develop high performance electrolytes.

Hydroxypropylmethylcellulose: Functional material carrier for in-situ solid electrolyte engineering of advanced lithium metal batteries

Electrolyte engineering strategies with convenient operation and conspicuous effect have been launched a lot for rechargeable lithium metal batteries (LMBs). However, something profitable for LMBs’ comprehensive performance is confined to its noxious reactions with the reactive lithium metal anode. Here, for the first time, a concept of functional material carrier is proposed. Due to the excellent H2O-anchoring and film-forming capacity, hydroxypropylmethylcellulose is designated as a H2O-carrier for decorating the hydrophobicity of polyolefin separator and promoting the in-situ polymerization of liquid electrolyte with the firmly-anchored trace H2O, while avoiding the direct contact between the reactive electrode and movement-restricted H2O. Using this modification, the lithium metal anode exhibits outstanding cyclic stability, and the high-loading LiNi0.6Co0.2Mn0.2O2-coupled LMBs present excellent capacity retention (above 72% over 500 cycles). Enlightening, this scalable carrier strategy can be further developed with synergistic effects of specific additives, accelerating the commercialization of sustainable, affordable, and secure LMBs.

Electrocatalyst Microenvironment Engineering for Enhanced Product Selectivity in Carbon Dioxide and Nitrogen Reduction Reactions.

Carbon and nitrogen fixation strategies are regarded as alternative routes to produce valuable chemicals used as energy carriers and fertilizers that are traditionally obtained from unsustainable and energy-intensive coal gasification (CO and CH4), Fischer-Tropsch (C2H4), and Haber-Bosch (NH3) processes. Recently, the electrocatalytic CO2 reduction reaction (CO2RR) and N2 reduction reaction (NRR) have received tremendous attention, with the merits of being both efficient strategies to store renewable electricity while providing alternative preparation routes to fossil-fuel-driven reactions. To date, the development of the CO2RR and NRR processes is primarily hindered by the competitive hydrogen evolution reaction (HER); however, the corresponding strategies for inhibiting this undesired side reaction are still quite limited. Considering such complex reactions involve three gas-liquid-solid phases and successive proton-coupled electron transfers, it appears meaningful to review the current strategies for improving product selectivity in light of their respective reaction mechanisms, kinetics, and thermodynamics. By examining the developments and understanding in catalyst design, electrolyte engineering, and three-phase interface modulation, we discuss three key strategies for improving product selectivity for the CO2RR and NRR: (i) targeting molecularly defined active sites, (ii) increasing the local reactant concentration at the active sites, and (iii) stabilizing and confining product intermediates.

Stabilization of non-noble metal electrocatalysts for acidic oxygen evolution reaction

Modern proton exchange membrane water electrolyzers rely on noble metal electrocatalysts. The application of Ir and Pt in such electrolyzers is considered a prerequisite for their long-term operation. However, the scarcity of these critical raw materials is the major drawback of this technology. In recent years, the academic community scrutinized the suitability of non-noble metals as alternative electrocatalysts. While these metals still demonstrate relatively low activity and stability, significant progress has been achieved in improving their performance. Here, we briefly overview recent achievements in oxygen evolution electrocatalysis using non-noble metals. We identify and discuss five stabilization strategies: (a) thermodynamic stabilization; (b) suppression of dissolution kinetics; (c) electrolyte engineering; (d) protection of active interfaces; and (e) system-level solutions. We provide critical remarks on the advantages and drawbacks of the strategies. Moreover, following our previous opinions in this journal, we highlight the significance of testing non-noble metal electrocatalysts in real devices.

Machine Learning Assisted Analysis of Electrochemical H2O2 Production

The two-electron water oxidation reaction (2e– WOR) provides an option for on-site production of the valuable chemical hydrogen peroxide (H2O2). A major challenge for the 2e– WOR is the need to improve its selectivity toward H2O2 over O2 production through the oxygen evolution reaction. Electrolyte engineering has shown great promise in improving the selectivity and production rates toward H2O2. However, experimental efforts in optimizing the electrolyte only yield results at discrete conditions, which does not provide a complete picture of performance over the entire parameter range. Here, we apply a machine learning assisted prediction to map out the performance of electrochemical H2O2 production over the continuous parameter space of electrolyte composition and applied potential. We collected experimental data of faradaic efficiencies (FEH2O2) and current densities toward H2O2 (JH2O2) as functions of the applied potential and carbonate ion mole fractions (HCO3– and CO32–) in the electrolyte. The data were then used to train a support vector regression model with 5-fold cross-validation. The accuracy of the model was verified against additional experimental results. The model identified that a maximum H2O2 current density of 2.16 mA/cm2 can be achieved from an optimized bicarbonate ion mole fraction of 0.225 at an applied potential of 3.25 V vs RHE. Lastly, the continuous model enables us to evaluate the thermal efficiency, H2O2 electricity cost, and time needed to produce a set amount of H2O2 over a broad range of electrolytes and applied potential conditions. This work demonstrates how machine learning enables the use of discrete experimental points to construct a continuous picture of electrochemical H2O2 production with high accuracy.

Reversible Li Plating on Graphite Anodes through Electrolyte Engineering for Fast-Charging Batteries.

The difficulties to identify the rate-limiting step cause the lithium (Li) plating hard to be completely avoided on graphite anodes during fast charging. Therefore, Li plating regulation and morphology control are proposed to address this issue. Specifically, a Li plating-reversible graphite anode is achieved via a localized high-concentration electrolyte (LHCE) to successfully regulate the Li plating with high reversibility over high-rate cycling. The evolution of solid electrolyte interphase (SEI) before and after Li plating is deeply investigated to explore the interaction between the lithiation behavior and electrochemical interface polarization. Under the fact that Li plating contributes 40 % of total lithiation capacity, the stable LiF-rich SEI renders the anode a higher average Coulombic efficiency (99.9 %) throughout 240 cycles and a 99.95 % reversibility of Li plating. Consequently, a self-made 1.2-Ah LiNi0.5 Mn0.3 Co0.2 O2 | graphite pouch cell delivers a competitive retention of 84.4 % even at 7.2 A (6 C) after 150 cycles. This work creates an ingenious bridge between the graphite anode and Li plating, for realizing the high-performance fast-charging batteries.

Reversible Li Plating on Graphite Anodes through Electrolyte Engineering for Fast‐Charging Batteries

AbstractThe difficulties to identify the rate‐limiting step cause the lithium (Li) plating hard to be completely avoided on graphite anodes during fast charging. Therefore, Li plating regulation and morphology control are proposed to address this issue. Specifically, a Li plating‐reversible graphite anode is achieved via a localized high‐concentration electrolyte (LHCE) to successfully regulate the Li plating with high reversibility over high‐rate cycling. The evolution of solid electrolyte interphase (SEI) before and after Li plating is deeply investigated to explore the interaction between the lithiation behavior and electrochemical interface polarization. Under the fact that Li plating contributes 40 % of total lithiation capacity, the stable LiF‐rich SEI renders the anode a higher average Coulombic efficiency (99.9 %) throughout 240 cycles and a 99.95 % reversibility of Li plating. Consequently, a self‐made 1.2‐Ah LiNi0.5Mn0.3Co0.2O2 | graphite pouch cell delivers a competitive retention of 84.4 % even at 7.2 A (6 C) after 150 cycles. This work creates an ingenious bridge between the graphite anode and Li plating, for realizing the high‐performance fast‐charging batteries.

Quantitative Description of Bubble Formation in Response to Electrolyte Engineering.

The green hydrogen economy is expected to play a crucial role in carbon neutrality, but industrial-scale water electrolysis requires improvements in efficiency, operation costs, and capital costs before broad deployment. Electrolysis operates at a high current density and involves the substantial formation of gaseous products from the electrode surfaces to the electrolyte, which may lead to additional resistance and a resulting loss of efficiency. A detailed clarification of the bubble departure phenomena against the electrode surface and the surrounding electrolytes is needed to further control bubbles in a water electrolyzer. This study clarifies how electrolyte properties affect the measured bubble detachment sizes from the comparisons with analytical expressions and dynamic simulations. Bubble behavior in various electrolyte solutions and operating conditions was described using various physical parameters. A quantitative relationship was then established to connect electrolyte properties and bubble departure diameters, which can help regulate the bubble management through electrolyte engineering.

Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts

Invited for this month's cover is the group of Dunwei Wang from Boston College and Serhiy Cherevko from the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy. The image illustrates the impact of different electrolyte environments on the stability of hematite decorated with an iridium molecular catalyst used for solar water splitting. The Research Article itself is available at 10.1002/cssc.202202319.

Front Cover: Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts (ChemSusChem 7/2023)

The Front Cover shows a date night between hematite and a molecular iridium catalyst used as a hybrid photoanode for solar water splitting. As the night progresses, the “stability” of their relationship evolves with it, spending their best time at around pH 9. Tuning the system parameters such as the electrolyte pH can have a great impact on the activity and stability of a photoelectrochemical system and should be chosen with care when designing advanced photoanodes. More information can be found in the Research Article by K. J. Jenewein et al.

Non-solvating fluorosulfonyl carboxylate enables temperature-tolerant lithium metal batteries

Advanced electrolyte engineering is an important strategy for developing high-efficacy lithium (Li) metal batteries (LMBs). Unfortunately, the current electrolytes limit the scope for creating batteries that perform well over temperature ranges. Here, we present a new electrolyte design that uses fluorosulfonyl carboxylate as a non-solvating solvent to form difluoroxalate borate (DFOB-) anion-rich solvation sheath, to realize high-performance working of temperature-tolerant LMBs. With this optimized electrolyte, favorable SEI and CEI chemistries on Li metal anode and nickel-rich cathode are achieved, respectively, leading to fast Li+ transfer kinetics, dendrite-free Li deposition and suppressed electrolyte deterioration. Therefore, Li||LiNi0.80Co0.15Al0.05O2 batteries with a thin Li foil (50 μm) show a long-term cycling lifespan over 400 cycles at 1C and a superior capacity retention of 90% after 200 cycles at 0.5C under 25 ℃. Moreover, this electrolyte extends the operating temperature from −10 to 30 ℃ and significantly improve the capacity retention and Coulombic efficiency of batteries are improved at high temperature (60 ℃). Fluorosulfonyl carboxylates thus have considerable potential for use in high-performance and all-weather LMBs, which broadens the new exploring of electrolyte design.

Electrolyte Engineering for Safer Lithium‐Ion Batteries: A Review

Comprehensive SummaryDespite being widely used in people's daily life, the safety issue of lithium‐ion batteries (LIBs) has become the major barrier for them to be applied in electrical vehicles (EVs) or large‐scale energy storage. Typically, due to the use of liquid electrolytes containing flammable solvents which are easily oxidized by excessive and accumulated heat, the potential thermal runaway is a major safety concern for traditional LIBs. A strategy for a safer electrolyte design is controlling the flammability and volatility of the liquid electrolytes, to effectively prevent thermal runaway, thus avoiding fire or other risks. Through this study, the mechanisms of thermal runaway and the recent progress in electrolyte engineering toward LIBs were summarized, covering the major strategies including adding flame‐retardants, the utilization of ionic liquid electrolytes and solid electrolytes. The characteristics, strengths and weaknesses of different strategies were discussed. New designing directions of safer electrolytes for the LIBs were also provided.

Electrolyte Engineering on Performance Enhancement of NiCo2 S4 Anode for Sodium Storage.

NiCo2 S4 is an attractive anode for sodium-ion batteries (SIBs) due to its high capacity and excellent redox reversibility. Practical deployment of NiCo2 S4 electrode in SIBs, however, is still hindered by the inferior capacity and unsatisfactory cycling performance, which result from the mismatch between the electrolyte chemistry and electrode. Herein, a functional electrolyte containing 1.0m NaCF3 SO3 in diethylene glycol dimethyl ether (DEGDME) (1.0m NaCF3 SO3 -DEGDME) is developed, which can be readily used for NiCo2 S4 anode with high initial coulomb efficiency (96.2%), enhanced cycling performance, and boosted capacities (341.7mA h g-1 after 250 continuous cycles at the current density of 200mA g-1 ). The electrochemical tests and related phase characterization combined with density functional theory (DFT) calculation indicate the ether-based electrolyte is more suitable for the NiCo2 S4 anode in SIBs due to the formation of a stable electrode-electrolyte interface. Additionally, the importance of the voltage window is also demonstrated to further optimize the electrochemical performance of the NiCo2 S4 electrode. The formation of sulfide intermediates during charging and discharging is predicted by combining DFT and verified by in situ XRD and HRTEM. The findings indicate that electrolyte engineering would be an effective way of performance enhancement for sulfides in practical SIBs.

Reconstructing the solvation structure and solid-liquid interface enables dendrite-free zinc-ion batteries

Dendrite growth and side reactions are culprits leading to the short lifespan and low Coulombic efficiency in aqueous Zn-ion batteries. Electrolyte engineering has been considered as the most facile and efficient strategy to overcome the above issues. Herein, introducing trace zinc gluconate to adjust the content of the strong H-bond in a conventional ZnSO4 electrolyte is proposed to achieve a stable Zn anode. Experimental measurements demonstrate that the solvation configuration around Zn ions has been evidently reconstructed due to the intensive coordination ability of gluconate anions. At the same time, gluconate anions electrostatically adsorb on the Zn metal surface, forming a new solid-liquid interface. As such, side reactions with water molecules and the self-corrosion of Zn metal have been significantly suppressed due to the newly formed solvation structure and interface, restraining the growth of dendrites. Impressively, the cycling life of the Zn||Zn symmetric cell in the modified electrolyte is able to sustain as long as 1500 h even at 5.0 mA cm−2. The as-assembled NH4V4O10||Zn full cell also realizes 1000 cycles with only 0.0049% capacity decay per cycle. This study offers a facile yet pragmatic route for the design of a multifunctional electrolyte for a superior stable Zn-metal anode.

Data-driven electrolyte design for lithium metal anodes

Improving Coulombic efficiency (CE) is key to the adoption of high energy density lithium metal batteries. Liquid electrolyte engineering has emerged as a promising strategy for improving the CE of lithium metal batteries, but its complexity renders the performance prediction and design of electrolytes challenging. Here, we develop machine learning (ML) models that assist and accelerate the design of high-performance electrolytes. Using the elemental composition of electrolytes as the features of our models, we apply linear regression, random forest, and bagging models to identify the critical features for predicting CE. Our models reveal that a reduction in the solvent oxygen content is critical for superior CE. We use the ML models to design electrolyte formulations with fluorine-free solvents that achieve a high CE of 99.70%. This work highlights the promise of data-driven approaches that can accelerate the design of high-performance electrolytes for lithium metal batteries.

Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts.

Molecular catalysts are promising oxygen evolution promoters in conjunction with photoanodes for solar water splitting. Maintaining the stability of both photoabsorber and cocatalyst is still a prime challenge, with many efforts tackling this issue through sophisticated material designs. Such approaches often mask the importance of the electrode-electrolyte interface and overlook easily tunable system parameters, such as the electrolyte environment, to improve efficiency. We provide a systematic study on the activity-stability relationship of a prominent Fe2 O3 photoanode modified with Ir molecular catalysts using in situ mass spectroscopy. After gaining detailed insights into the dissolution behavior of the Ir cocatalyst, a comprehensive pH study is conducted to probe the impact of the electrolyte on the performance. An inverse trend in Fe and Ir stability is found, with the best activity-stability synergy obtained at pH 9.7. The results bring awareness to the overall photostability and electrolyte engineering when advancing catalysts for solar water splitting.

Recent Advances in Potassium‐Ion Batteries: From Material Design to Electrolyte Engineering

AbstractCompared with extensively applied lithium‐ion batteries, potassium‐ion batteries (PIBs) exhibit similar working principles, comparable energy densities but low costs and thus great potential in grid‐scale energy storage applications. However, the K‐storage performance of PIBs is significantly limited by the serious structure stress in electrode materials due to the large radius of K+ as well as poor electrolyte design principles to match the novel energy storage system. This review summarizes recent advances in material design of cathode and anode electrodes as well as electrolyte engineering for the novel electrochemical K‐storage system. Especially the rational manipulation of the solid electrolyte interphase by electrolyte design to achieve satisfactory K‐storage performance is emphasized. Furthermore, the guidelines and improved strategies are proposed for developing advanced PIBs for next‐generation energy storage technologies.

Toward High Energy Density FeFx (x=2 and 3) Cathodes for Lithium‐Ion Batteries

AbstractIt has been challenging to develop next‐generation higher energy density cathode materials to satisfy the incremental demand for lightweight and miniaturization for lithium‐ion batteries (LIBs). The iron‐based fluoride (FeFx) cathodes may be highly competitive due to abundant resources as well as high theoretical capacity. However, the complex multiphase conversion reactions of the FeFx cathodes cause limited battery performance hindering its commercialization. Herein, this review focuses on the multi‐electron conversion processes involved in solid‐solid reactions. More importantly, the scientific strategies of enhanced FeFx performance are mainly addressed in view of four critical aspects, i. e., conductive matrix, heteroatom doping, surface modification, and electrolyte engineering. It is demonstrated that the optimized strategies can mitigate the challenges of the FeFx cathodes during multi‐electron conversion processes. It is believed that this review has been a guidance for improving the cycling performance of the FeFx cathodes for high energy density LIBs.

Low-Temperature Working Feasibility of Zinc–Air Batteries with Noble Metal-Free Electrocatalysts

Open AccessRenewablesRESEARCH ARTICLES23 Jan 2023Low-Temperature Working Feasibility of Zinc-Air Batteries with Noble-Metal-Free Electrocatalysts Chang-Xin Zhao, Jia-Ning Liu, Nan Yao, Xiaoyuan Zeng, Aibing Chen, Peng Dong, Yingjie Zhang, Xinzhi Ma, Cheng Tang, Bo-Quan Li and Qiang Zhang Chang-Xin Zhao Google Scholar More articles by this author , Jia-Ning Liu Google Scholar More articles by this author , Nan Yao Google Scholar More articles by this author , Xiaoyuan Zeng Google Scholar More articles by this author , Aibing Chen Google Scholar More articles by this author , Peng Dong Google Scholar More articles by this author , Yingjie Zhang Google Scholar More articles by this author , Xinzhi Ma Google Scholar More articles by this author , Cheng Tang Google Scholar More articles by this author , Bo-Quan Li Google Scholar More articles by this author and Qiang Zhang Google Scholar More articles by this author https://doi.org/10.31635/renewables.023.202300026 SectionsSupplemental MaterialAboutPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Expanding the application scenario for rechargeable batteries is the key to the terminal utilization of renewable energy. Enabling zinc-air batteries at low temperatures is drawing increasing attention, yet the low-temperature working feasibility of zinc-air batteries with noble-metal-free electrocatalysts remains indistinct. In this contribution, the low-temperature performances of zinc-air batteries with noble-metal-free electrocatalysts are comprehensively investigated. Armed with a representative noble-metal-free bifunctional oxygen electrocatalyst, the zinc-air batteries demonstrate satisfactory yet relatively declined performance at low temperatures, compared with that at room temperatures. The reduced electrolyte conductivity is identified as one of the limiting factors for the reduced low-temperature performances. Furthermore, electrolyte engineering via regulating the solvation structure is performed on the zinc-air batteries with noble-metal-free electrocatalysts, where a promoted low-temperature performance is achieved. This work reveals the compatibility between noble-metal-free electrocatalysts and low-temperature feasibility/low-temperature performance enhancement strategies for zinc-air batteries and affords new opportunities to satisfy low-cost and efficient energy storage at harsh working conditions. Download figure Download PowerPoint Next article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2023 Chinese Chemical Society Downloaded 0 times PDF downloadLoading ...

In-Depth Insight into a Passive Film through Hydrogen-Bonding Network in an Aqueous Zinc Battery

Electrochemical stability and interfacial reactions are crucial for rechargeable aqueous zinc batteries. Electrolyte engineering with low-cost aqueous electrolytes is highly required to stabilize their interfacial reactions. Herein, we propose a design strategy using glutamic additive and its derivatives with modification of hydrogen-bonding network to enable Zn aqueous battery at a low concentration (2 m ZnSO4 + 1 m Li2SO4). Computational, in situ/ex situ spectroscopic, and electrochemical studies suggest that additives with moderate interactions, such as 0.1 mol % glutamic additive (G1), preferentially absorb on the Zn surface to homogenize Zn2+ plating and favorably interact with Zn2+ in bulk to weaken the interaction between H2O and Zn2+. As a result, uniform deposition and stable electrochemical performance are realized. The Zn||Cu half-cell lasts for more than 200 cycles with an average Coulombic efficiency (CE) of >99.32% and the Zn||Zn symmetrical cells for 1400 h with a low and stable overpotential under a current density of 0.5 mA cm-2, which is better than the reported results. Moreover, adding 0.1 mol % G1 to the Zn||LFP full cell improves its electrochemical performance with stable cycling and achieves a remarkable capacity of 147.25 mAh g-1 with a CE of 99.79% after 200 cycles.