Electrode-electrolyte Interphase Research Articles

Unraveling the Multifunctional Mechanism of Fluoroethylene Carbonate in Enhancing High-Performance Room-Temperature Sodium-Sulfur Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries has attracted growing attentions in large-scale energy storage technology, while the serious shuttle effect and interface side reaction limit its practical application. Despite fluoroethylene carbonate (FEC) has been widely used as an electrolyte additive or co-solvent to facilitate the optimization of electrode-electrolyte interphase in RT Na-S batteries, its crucial influence and mechanism have not been clearly understood. Herein, we deeply reveal the two-steps cathode-electrolyte interphase (CEI) formation by using FEC as the exclusive electrolyte solvent. The results demonstrate that FEC participates in both rapid nucleophilic reaction and electrochemical decomposition on cathode, which can effectively in situ construct a unique "chocolate-cookie" shaped CEI consisted of NaF-rich double layers. This CEI eliminates the shuttle effect and ensures the solid-solid conversion of sulfur. Along with the stable F-rich solid-electrolyte interphase (SEI) formed on the Na anode, the RT Na-S battery delivers an impressive performance (456 mAh g-1 after 1000 cycles at 0.5 C) with almost 100% Coulombic efficiency. This significantly simplifies electrolyte design and provides valuable insights into the application of FEC in practical Na-S batteries.

Building electrode/electrolyte interphases in aqueous zinc batteries via self-polymerization of electrolyte additives

Abstract Aqueous zinc batteries offer promising prospects for large-scale energy storage, yet their application is limited by undesired side reactions at the electrode-electrolyte interface. Here, we report a universal approach for in situ building an electrode/electrolyte interphase (EEI) layer on both the cathode and anode through the self-polymerization of electrolyte additives. In an exemplified Zn||V2O5·nH2O cell, we reveal that the glutamate additive undergoes radical-initiated electro-polymerization on the cathode and polycondensation on the anode, yielding polyglutamic acid-dominated EEI layers on both electrodes. These EEI layers effectively mitigate undesired interfacial side reactions while enhance reaction kinetics, enabling Zn||V2O5·nH2O cell to achieve a high capacity of 387 mAh g−1 at 0.2 A g−1 and maintain over 96.3% capacity retention after 1500 cycles at 1 A g−1. Moreover, this interphase-forming additive exhibits broad applicability to varied cathode materials, encompassing VS2, VS4, VO2, α-MnO2, β-MnO2, and δ-MnO2. The methodology of utilizing self-polymerizable electrolyte additives to construct robust EEI layers opens a novel pathway of interphase engineering for electrode stabilizing in aqueous batteries.

In Situ Formed Continuous and Dense Inorganic Borate-Based SEI for High-Performance Li-Metal Batteries.

The practical application of lithium metal batteries (LMBs) is largely hindered by the notorious lithium dendrite growth, low cycle efficiency associated with insufficient electrode-electrolyte interphase dynamics, and electrolyte combustion. Here, an advanced electrolyte using a combination of three kinds of salts dissolved in carbonate-based solvents is developed. The salt anions dominate a primary solvation sheath, resulting in weak interaction between Li+ and the solvents, as well as the in situ formation of an inorganic-rich bilayer solid electrolyte interface (SEI). The designed electrolyte enables high cycle stability in LMBs with a high-loading NMC cathode (approximately 20mg cm-2), exhibiting 89.89% capacity retention after 200 cycles with the cutoff voltage of 4.5V. Cryo-TEM characterization and density-functional theory (DFT) calculations reveal that the borate-based bilayer SEI, characterized by an exceptional dense structure, effectively suppresses lithium dendrite growth, and certify the crucial role of inorganic component continuity and density within the SEI, which surpasses the absorption and migration energy barrier in terms of significance. This profound understanding of SEI structure holds great potential for advancing the development of high-stable LMBs and can be expanded to other battery system.

Cosolvent electrolyte chemistries for high-voltage potassium-ion battery.

The poor oxidation resistance of traditional electrolytes has hampered the development of high-voltage potassium-ion battery technology. Here, we present a cosolvent electrolyte design strategy to overcome the high-voltage limitations of potassium-ion electrolyte chemistries. The cosolvent electrolyte breaks the dissolution limitation of the salt through ion-dipole interactions, significantly enlarging the anion-rich solvation clusters, as verified by the insitu synchrotron-based wide-angle X-ray scattering experiments. Furthermore, the large anion-rich solvation clusters also facilitate the formation of an effective electrode-electrolyte interphase, thereby enhancing compatibility with high-voltage electrodes. The cosolvent electrolyte enables K||Prussian blue cells (2-4.5V) to operate for >700 cycles with a capacity retention of 91.9%. Our cosolvent electrolyte design strategy paves new avenues for the development of high-voltage potassium-ion batteries and beyond.

Uncovering the Crucial Role of Chelating Structures in Cyano-Alkyl-Phosphate Electrolytes for High-Voltage Lithium Metal Batteries.

The inferior oxidative stability of commercial carbonate electrolytes and overgrowth of the electrode-electrolyte interphase (EEI) have largely hindered the development of high-voltage lithium metal batteries. In this study, these challenges are addressed by designing Li+-solvent chelating solvation structures to inhibit solvent decomposition using cyano-alkyl-phosphate as a demonstration. Theoretical and experimental studies confirm that the -P═O and -C≡N groups within diethyl (2-cyanethyl) phosphonate exhibit a comparable ability to coordinate with Li+, facilitating the formation of seven-membered chelating structures. This unique solvation structure contributes to the formation of anion-derived inorganic-rich EEI with high stability and robustness, hindering the further decomposition of the electrolyte. Additionally, the cyano group has a strong complexation with the transition metal (TM) in the cathode to inhibit TM dissolution, thereby ensuring the structural stability of the cathode particle. Utilizing this special chelating structure, the designed electrolyte demonstrates favorable Li plating/stripping reversibility and promising oxidative stability in high-voltage batteries. Consequently, the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode exhibits a high capacity retention (90%) after operating 300 cycles. Under harsh testing conditions, the 4.6 V Li||NCM811 pouch cell with a capacity of 1.4 Ah (∼295 Wh kg-1 based on the total mass of the cell) retains 70% capacity after 80 cycles. This work provides new insights into the correlation between the solvation structure and oxidative stability of electrolytes, contributing significantly to the advancement of high-voltage lithium metal batteries.

Cathode-Electrolyte Interphase Engineering toward Fast-Charging LiFePO4 Cathodes by Flash Carbon Coating.

Lithium iron phosphate (LiFePO4, LFP) batteries are widely used in electric vehicles and energy storage systems due to their excellent cycling stability, affordability and safety. However, the rate performance of LFP remains limited due to its low intrinsic electronic and ionic conductivities. In this work, an ex situ flash carbon coating method is developed to enhance the interfacial properties for fast charging. A continuous, amorphous carbon layer is achieved by rapidly decomposing the precursors and depositing carbon species in a confined space within 10 s. Simultaneously, different heteroatoms can be introduced into the surface carbon matrix, which regulates the irregular growth of cathode-electrolyte interphase (CEI) and selectively facilitates the inorganic region formation. The inorganic-rich, hybrid conductive CEI not only promotes electron and ion transport but also restricts parasitic side reactions. Consequently, LFP cathodes with fluorinated carbon coatings exhibited the highest capacity of 151 mAh g-1 at 0.2 C and 96mAhg-1 at 10 C, indicating their excellent rate capability over commercial LFP (58mAh g-1 at 10 C). This solvent-free, versatile surface modification is shown for other electrode materials, providing an efficient platform for electrode-electrolyte interphase engineering through a surface post-treatment.

Ether-Based Gel Polymer Electrolyte for High-Voltage Potassium Ion Batteries.

Low-concentration ether electrolytes cannot efficiently achieve oxidation resistance and excellent interface behavior, resulting in severe electrolyte decomposition at a high voltage and ineffective electrode-electrolyte interphase. Herein, we utilize sandwich structure-like gel polymer electrolyte (GPE) to enhance the high voltage stability of potassium-ion batteries (PIBs). The GPE contact layer facilitates stable electrode-electrolyte interphase formation, and the GPE transport layer maintains good ionic transport, which enabled GPE to exhibit a wide electrochemical window and excellent electrochemical performance. In addition, Al corrosion under a high voltage is suppressed through the restriction of solvent molecules. Consequently, when using the designed GPE (based on 1 m), the K||graphite cell exhibits excellent cycling stability of 450 cycles with a capacity retention of 91%, and the K||FeFe-Prussian blue cell (2-4.2 V) delivers a high average Coulombic efficiency of 99.9% over 2200 cycles at 100 mA g-1. This study provides a promising path in the application of ether-based electrolytes in high-voltage and long-lasting PIBs.

Weakly solvating ester electrolyte for high voltage sodium-ion batteries

Ethyl acetate (EA) was identified as a promising electrolyte solvent for sodium-ion batteries (SIBs), exhibiting low viscosity, cost-effectiveness, and low toxicity. Despite a significant portion of aggregation being linked to the weak solvation of Na+/EA as revealed by molecular dynamics (MD) simulations, pulsed-field gradient nuclear magnetic resonance (pfg-NMR) analysis identified a noteworthy Na+ diffusion coefficient of 3.95×10−10 m2 s−1 at 25°C in the presence of 1 m NaPF6 salt. Employing fluoroethylene carbonate (FEC) as a film-forming additive to create electrode-electrolyte interphase, this electrolyte surprisingly made ∼210 mAh Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2 (NCMFNZO)/hard carbon (HC) pouch cells achieve a lengthy cycling lifetime of 250 cycles with ∼80 % capacity retention, cycled up to 4.0 V at 40°C. X-ray photoelectron spectroscopy (XPS) revealed increasing interphasial organic species over cycling, augmenting charge transfer resistance on both cathode and anode, particularly during fast charging or low temperatures (<10°C), promoting Na plating. Gas chromatography-mass spectrometry combined with density functional theory identified CO2 as the major gas generated from charged cathode/electrolyte interactions, exhibiting temperature/voltage dependence.

In-situ dynamic catalysis electrode electrolyte interphase enabling Mg2+ insertion in 2D metal–organic polymer for high-capacity and long-lifespan magnesium batteries

Rechargeable magnesium battery is regarded as the promising candidate for the next generation of high-specific-energy storage systems. Nevertheless, issues related to severe Mg-Cl dissociation at the electrolyte–electrode interface impede the insertion of Mg2+ into most materials, leading to severe polarization and low utilization of Mg-storage electrodes. In this study, a metal–organic polymer (MOP) Ni-TABQ (Ni-coordinated tetramino-benzoquinone) with superior surface catalytic activity is proposed to achieve the high-capacity Mg-MOP battery. The layered Ni-TABQ cathode, featuring a unique 2D π-d linear conjugated structure, effectively reduces the dissociation energy of MgxCly clusters at the Janus interface, thereby facilitating Mg2+ insertion. Due to the high utilization of active sites, Ni-TABQ achieves high capacities of 410 mAh/g at 200 mA g−1, attributable to a four-electron redox process involving two redox centers, benzoid carbonyls, and imines. This research highlights the importance of surface electrochemical processes in rechargeable magnesium batteries and paves the way for future development in multivalent metal-ion batteries.

Stable interphase inducer based on montmorillonite clay mineral to enhance stability and fire safety for lithium metal batteries

Heat buildup from factors like mechanical, electrical, or thermal stress is the main safety issue in lithium metal batteries (LMBs). Even without such stressors, however, LMBs may remain fire-prone because of the development of unstable electrode–electrolyte interphase on charge–discharge, potentially leading to internal short circuits. In this study, a stable cathode-electrolyte interphase inducer (SCEI-I) is proposed to tackle both the cycling stability issue and safety concerns. SCEI-I is synthesized by incorporating montmorillonite, a clay mineral, and methylphosphonic acid dimethyl ester, a flame-retardant material, onto a porous polyethylene film. On cycling, SCEI-I can induce a thin (<8 nm), uniform and robust cathode-electrolyte interphase layer, contributing to a steady and high Coulombic efficiency of 99.6%–99.8% with decreased impedance. SCE-I improves electrochemical performance by reducing the capacity degradation from ∼21.9% to ∼8.9% after 100 cycles. SCE-I also demonstrates strong thermal stability as the endothermic energy of SCEI-I is only –32.4 J/g (24 °C–280 °C), which is less than one-third of that of polypropylene separator (–118.9 J/g). Furthermore, when exposed to fire, the SCEI-I membrane instantly extinguished flames by disrupting combustion chain reaction. The present study proposes an interfacial engineering approach to improve the stability and safety of LMBs.

Constructing sulfur-rich interphase to promote the cycle stability of graphite/LiNi0.8Co0.1Mn0.1O2 pouch battery at elevated temperature

Lithium-ion batteries (LIBs) with LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes have a high energy density, but their long-cycle performance, especially at high temperature, should still be improved due to the instability of the NCM811 cathode-electrolyte interphase. In this work, 2, 2, 2-Trifluoroethyl p-Toluenesulfonate (TPTS) is introduced as a functional film-forming electrolyte additive design to improve the long-term stability of graphite/NCM811 batteries. The preferential redox reactions of TPTS molecules play a pivotal role in fostering the creation of a sulfur-riched interphase, characterized by low impedance. This interphase works to fortify the interfacial structure, effectively inhibiting the dissolution of transition metal ions. Therefore, in comparison to the graphite/NCM811 pouch batteries lacking additive, TPTS enhance the long-cycle capacity retention from 47 % to 80 % after 450 cycles at 45 °C. What's more, TPTS suppresses outgassing and demonstrates enhanced capacity maintenance for the battery even after storage at 60 °C. This work not only demonstrates the stabilizing impacts of TPTS on the electrode-electrolyte interphase and its enhancement of cycling performance at elevated temperatures but also introduces a novel approach for the practical utilization of functional electrolytes matching high-nickel LIBs.

Nonflammable Succinonitrile-Based Deep Eutectic Electrolyte for Intrinsically Safe High-Voltage Sodium-Ion Batteries.

Intrinsically safe sodium-ion batteries are considered as a promising candidate for large-scale energy storage systems. However, the high flammability of conventional electrolytes may pose serious safety threats and even explosions. Herein, a strategy of constructing a deep eutectic electrolyte is proposed to boost the safety and electrochemical performance of succinonitrile (SN)-based electrolyte. The strong hydrogen bond between S═O of 1,3,2-dioxathiolane-2,2-dioxide (DTD) and the α-H of SN endows the enhanced safety and compatibility of SN with Lewis bases. Meanwhile, the DTD participates in the inner Na+ sheath and weakens the coordination number of SN. The unique solvation configuration promotes the formation of robust gradient inorganic-rich electrode-electrolyte interphase, and merits stable cycling of half-cells in a wide temperature range, with a capacity retention of 82.8% after 800 cycles (25°C) and 86.3% after 100 cycles (60°C). Correspondingly, the full cells deliver tremendous improvement in cycling stability and rate performance.

Electrolyte solvent composition regulating endows CoSe2 hollow nanocage anode with stable potassium ion storage

Metal selenides are ideal anode materials for potassium-ion batteries (PIBs) due to their significant merits of favorable conductivity and ion transport property. However, the inevitable volume changes of metal selenides electrode during potassiation/depotassiation processes result in the fracture and reconstruction of the solid electrolyte interphase (SEI) layer, causing capacity decay and significantly limiting their practical applications. Reasonable morphology control accompanied by uniform and rigid SEI layer formation are key factors in improving the electrochemical cycling stability of metal selenides. In this paper, nano-hollow CoSe2 (CoSe2@CNC) anode materials are prepared using ZIF-67 as the precursor. The differences of electrochemical performances for CoSe2@CNC anode material in ester-based and ether-based electrolytes have been investigated in detail. Results demonstrate that the SEI layer formed in the ester-based electrolyte is loose and thick, leading to electrode pulverization and material detachment after several cycles, resulting in rapid degradation of cycle performance. In contrast, a thin and inorganic-rich SEI layer containing more inorganic components is formed in the ether-based electrolyte, effectively protecting the electrode from damage, facilitating electronic transfer at the electrode electrolyte interphase, and optimizing potassium ions storage performance.

Novel sulfur-based electrolyte additive for constructing high-quality sulfur-containing electrode-electrolyte interphase films in sodium-ion batteries

Sodium-ion batteries (SIBs) have been considered as the most promising grid-scale energy storage devices following lithium-ion batteries (LIBs). Similar to LIBs, the electrode–electrolyte interphase significantly impacts the cycling performance of the battery, and the presence of high-quality interphase films can greatly enhance the cycling performance of SIBs. In response to the interphase film challenges for SIBs, the investigation proposes the use of the sulfur-based additive 1,3-propanediol cyclic sulfate (PCS) to construct high-quality interphase films for improving electrochemical performance. Density functional theory (DFT) calculations indicate that PCS can preferentially undergo reduction–oxidation (Redox) reactions in conventional ester-based electrolyte systems, thereby forming sulfur-rich high-quality interphase films. The experimental results show that the capacity retention of NaNi1/3Fe1/3Mn1/3O2 (NFM)||hard carbon (HC) pouch cells increase from 33.94 % to 77.56 % after 300 cycles of long-term cycling at a current density of 0.5 C. Although the addition of PCS slightly reduces the ionic conductivity of the electrolyte (7.70 mS cm−1 vs. 8.09 mS cm−1), it lowers the activation energy (1.09 eV vs. 1.20 eV) and increases the Na+ transfer number (0.721 vs. 0.707) of the electrolyte, thereby improving the rate capability of NFM||HC pouch cells. This study demonstrates the potential application of PCS in SIBs and presents a forward-looking approach for exploring the film formation mechanism of sulfur-based additives.

Fluorinated solvent molecule tuning to improve electrochemical performances of low-concentration electrolyte

The development of low-concentration electrolyte has a favorable application prospect due to its advantages of saving lithium resources. However, the large-scale application is limited by the formation of high-impedance organic electrode/electrolyte interphase (EEI) and the higher desolvation energy of Li+. Herein, a mixed flurorinated solvents of ethyl difluoroacetate (2F) / ethyl trifluoroacetate (3F) (3:7, in volume ratio) is designed to adjust the interaction between Li+ and the solvents, so as to achieve performance improvements of the low-concentration electrolyte system containing 0.5 M LiPF6. Results shows that 2F solvent greatly weakens the interaction between Li+ and the solvents, and 3F solvent further promotes anions to enter the solvation sheath to form Li(2F)3.0(PF6−)2.3(3F)0.5 structure. It promotes the Li+ desolvation, and brings about the formation of a LiF-rich cathode-electrolyte interface film on the surface of LiFePO4 (LFP) cathode due to the HOMO of the 2F solvent in the solvation sheath of Li+ will be increase as the involvement of PF6− in the solvation sheath of Li+. As a result, the cycling stability and rate performance (130 mAh g−1 at 4 C) of the LFP/Li half-cell are significantly improved. This work provides a new strategy to improve the electrochemical performances of low-concentration electrolytes by fluorinated solvent molecule tuning.

Dual-Salt Electrolyte Additive Enables High Moisture Tolerance and Favorable Electric Double Layer for Lithium Metal Battery.

The carbonate electrolyte chemistry is a primary determinant for the development of high-voltage lithium metal batteries (LMBs). Unfortunately, their implementation is greatly plagued by sluggish electrode interfacial dynamics and insufficient electrolyte thermodynamic stability. Herein, lithium trifluoroacetate-lithium nitrate (LiTFA-LiNO3 ) dual-salt additive-reinforced carbonate electrolyte (LTFAN) is proposed for stabilizing high-voltage LMBs. We reveal that 1) the in situ generated inorganic-rich electrode-electrolyte interphase (EEI) enables rapid interfacial dynamics, 2) TFA- preferentially interacts with moisture over PF6 - to strengthen the moisture tolerance of designed electrolyte, and 3) NO3 - is found to be noticeably enriched at the cathode interface on charging, thus constructing Li+ -enriched, solvent-coordinated, thermodynamically favorable electric double layer (EDL). The superior moisture tolerance of LTFAN and the thermodynamically stable EDL constructed at cathode interface play a decisive role in upgrading the compatibility of carbonate electrolyte with high-voltage cathode. The LMBs with LTFAN realize 4.3 V-NCM523/4.4 V-NCM622 superior cycling reversibility and excellent rate capability, which is the leading level of documented records for carbonate electrode.

Dual‐Salt Electrolyte Additive Enables High Moisture Tolerance and Favorable Electric Double Layer for Lithium Metal Battery

AbstractThe carbonate electrolyte chemistry is a primary determinant for the development of high‐voltage lithium metal batteries (LMBs). Unfortunately, their implementation is greatly plagued by sluggish electrode interfacial dynamics and insufficient electrolyte thermodynamic stability. Herein, lithium trifluoroacetate‐lithium nitrate (LiTFA−LiNO3) dual‐salt additive‐reinforced carbonate electrolyte (LTFAN) is proposed for stabilizing high‐voltage LMBs. We reveal that 1) the in situ generated inorganic‐rich electrode‐electrolyte interphase (EEI) enables rapid interfacial dynamics, 2) TFA− preferentially interacts with moisture over PF6− to strengthen the moisture tolerance of designed electrolyte, and 3) NO3− is found to be noticeably enriched at the cathode interface on charging, thus constructing Li+‐enriched, solvent‐coordinated, thermodynamically favorable electric double layer (EDL). The superior moisture tolerance of LTFAN and the thermodynamically stable EDL constructed at cathode interface play a decisive role in upgrading the compatibility of carbonate electrolyte with high‐voltage cathode. The LMBs with LTFAN realize 4.3 V‐NCM523/4.4 V‐NCM622 superior cycling reversibility and excellent rate capability, which is the leading level of documented records for carbonate electrode.

Surface analysis insight note: Accounting for X‐ray beam damage effects in positive electrode‐electrolyte interphase investigations

We investigated the effects of X‐ray beam damage during X‐ray photoelectron spectroscopy measurement on LiNiO2 electrodes. The degree of damage induced by lab‐based and synchrotron X‐ray radiation has been compared between pristine and cycled electrodes, highlighting the role of positive solid electrode–electrolyte interphase to protect the cycled LiNiO2 surface from beam damage. The possible steps to avoid or at least reduce the beam‐induced effects are outlined.

Effect Temperature for improving the Li-ion conductivity of Li7La3Zr2O12

This study investigates the dissociation behavior of water-soluble salts of Li and La and the unique behavior of Zr sources, resulting in the generation of Li+, La3+, and Zr4+ ions in aqueous solutions. The specific conductivity of calcined SG1 and SG2 displays temperature-dependent variations, with SG1 consistently exhibiting higher conductivity (2.08 x 10-4 S/cm) across the temperature range. The closed-packed structure facilitates the controllable mass transfer of lithium, enhancing ionic conductivity. The constructed LiFePO4/LLZO/AC device using these electrolytes demonstrates an impressive energy density of 1.95 Wh/kg and a power density of 144.92 W/kg, showcasing an excellent solid electrode-electrolyte interphase. Over 10,000 cycles, cyclic stability, with an average performance of 86%, underscores the potential of LLZO as a solid electrolyte for advanced energy storage devices. The sol-gel synthesis and densification strategy is a simple and effective method for obtaining lithium-rich LLZO electrolytes. The enhanced ionic conductivity and electrochemical performance of the solid-state device emphasize the practical viability of this approach, contributing to the sustainable development of advanced energy storage technologies.

Additive‐guided Solvation‐regulated Flame‐retardant Electrolyte Enables High‐voltage Lithium Metal Batteries with Robust Electrode Electrolyte Interphases

AbstractWidening the voltage window of the nickel‐rich layered oxide cathode‐based lithium metal batteries (LMBs) can effectively improve the energy density of rechargeable batteries. However, serious safety issues associated with the high reactivity between LiNi0.8Co0.1Mn0.1O2 (NCM811) and electrolyte at high cut‐off voltage remains challenging. Herein, a flame‐retardant electrolyte with the ability to form a robust armor‐like electrode electrolyte interphase (EEI) with LiF and LixByOz compounds for stabilizing Li||NCM811 batteries is proposed. Such electrolyte exhibits the high thermal stability with flame‐retardant effect for ensuring the battery safety at high voltage. The armor‐like EEI can effectively protect both NCM811 and lithium (Li) for improving the battery cycling performance. As a result, the capacity retention rate of the NCM811 cathode with such electrolyte reached 68% after 150 cycles at 4.6 V. This work provides an effective reference for the reasonable design of high‐voltage, flame‐retardant electrolytes for LMBs.