Solid Electrolyte Interphase Research Articles

Tracking solid electrolyte interphase dynamics using operando fibre-optic infra-red spectroscopy and multivariate curve regression

As batteries drive the transition to electrified transportation and energy systems, ensuring their quality, reliability, lifetime, and safety is crucial. While the solid electrolyte interphase (SEI) is known to govern these performance characteristics, its dynamic nature makes understanding its nucleation, growth, and composition an ambitious, yet elusive aspiration. This work employs chalcogenide fibres embedded in negative electrode materials for operando Infra-red Fibre-optic Evanescent Wave Spectroscopy (IR-FEWS), combined with Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) algorithms for spectra analysis. By establishing molecular fingerprints that can be used to identify reaction products, IR-FEWS combined with MCR-ALS enables improved understanding of SEI evolution during cell formation with notable differences stemming from electrolyte or anode material. For example, despite operating at an elevated potential, lithium titanate’s SEI has intrinsic instability, evidenced by continued carbonate formation. This approach leads the hunt for the SEI down a new path, giving empirical formulations theoretical roots.

Synergistic Modulation of Solid- and Cathode-Electrolyte Interphase via a Lithium Salt Additive toward Stable Sodium Metal Batteries.

Constructing feasible sodium metal batteries (SMBs) faces complex challenges in stabilizing cathodes and sodium metal anodes. It is imperative, but often underemphasized, to simultaneously regulate the solid-electrolyte interphase (SEI) to counter dendrite growth and the cathode-electrolyte interphase (CEI) to mitigate cathode deterioration. Herein, we introduce lithium 2-trifluoromethyl-4,5-dicyanoimidazolide (LiTDI) as an efficacious additive in a carbonate-based electrolyte to extend cycle lifespan of full SMBs: the capacity retention reaches 77.8% after 8000 cycles at room temperature and 74.3% after 5000 cycles at 50 °C. Cryogenic transmission electron microscopy characterization reveals that LiTDI promotes formation of inorganics-condensed SEI and CEI. The former inhibits continuous electrolyte decomposition and ensures homogeneous sodium plating, while the latter shields cathode from transition metal dissolution. This study highlights the crucial role of LiTDI in stabilizing both anodes and cathodes in SMBs, and it provides insights into designing functional additives for synergistic modulation of SEI and CEI.

Multivariate Approaches Boosting Lithium-Mediated Ammonia Electrosynthesis in Different Electrolytes.

Ammonia electrosynthesis through the lithium-mediated approach has recently reached promising results towards high activity and selectivity in aprotic media, reaching high Faradaic efficiency (FE) values and NH3 production rates. To fasten the comprehension and optimization of the complex lithium-mediated nitrogen reduction system, for the first time a multivariate approach is proposed as a powerful tool to reduce the number of experiments in comparison with the classical one-factor-at-a-time approach. Doehlert design and surface response methodology are employed to optimize the electrolyte composition for a batch autoclaved cell. The method is validated with the common LiBF4 salt, and the correlations between the FE and the amount of lithium salt and ethanol as proton donor are elucidated, also discussing their impact on the solid electrolyte interphase (SEI) layer. Moreover, a new fluorinated salt is proposed (i.e., lithium difluoro(oxalate) borate (LiFOB)), taking inspiration from lithium batteries. This salt is chosen to tailor the SEI layer, with the aim of obtaining a bifunctional interfacial layer, both stable and permeable to N2, the latter being an essential characteristic for batch systems. The SEI layer composition is confirmed strategic and its tailoring with LiFOB boosts FE values.

Deciphering and Enhancing Rate‐Determining Step of Sodium Deposition towards Ultralow‐Temperature Sodium Metal Batteries

Achieving high ionic conductivity and stable performance at low temperatures remains a significant challenge in sodium‐metal batteries (SMBs). In this study, we propose a novel electrolyte design strategy that elucidates the solvation structure‐function relationship within mixed solvent systems. A mixture of diglyme and 1,3‐dioxolane was developed to optimize the solvation structure towards superior low‐temperature electrolyte. Molecular dynamics simulations and Raman spectra results reveal the solvent‐separated ion pairs and contact ion pairs dominated solvation structure in the designed electrolyte, displaying a superior ionic conductivity of 1.78×10‐3 S cm‐1 at ‐40 °C. Besides, comprehensive kinetic analysis shows Na+ transportation in the electrolyte shows a greater impact on sodium plating than Na+ transport through the solid electrolyte interphase or charge transfer. As a result, the electrolyte enables stable operation for over 12,000 hours in Na||Na cells at ‐40 °C. In Na||Na2/3Ni1/4Cu1/12Mn2/3O2 full cells, it maintains a high capacity retention of 92.4% over 600 cycles with an initial specific capacity of 89.4 mAh g‐1 at ‐40 °C, and achieves 81.7% capacity retention after 50 cycles with an initial specific capacity of 75.3 mAh g‐1 at ‐78 °C. These results pave the way for the development of high‐performance SMBs capable of operating under ultralow temperatures.

Deciphering and Enhancing Rate-Determining Step of Sodium Deposition towards Ultralow-Temperature Sodium Metal Batteries.

Achieving high ionic conductivity and stable performance at low temperatures remains a significant challenge in sodium-metal batteries (SMBs). In this study, we propose a novel electrolyte design strategy that elucidates the solvation structure-function relationship within mixed solvent systems. A mixture of diglyme and 1,3-dioxolane was developed to optimize the solvation structure towards superior low-temperature electrolyte. Molecular dynamics simulations and Raman spectra results reveal the solvent-separated ion pairs and contact ion pairs dominated solvation structure in the designed electrolyte, displaying a superior ionic conductivity of 1.78×10-3 S cm-1 at -40 °C. Besides, comprehensive kinetic analysis shows Na+ transportation in the electrolyte shows a greater impact on sodium plating than Na+ transport through the solid electrolyte interphase or charge transfer. As a result, the electrolyte enables stable operation for over 12,000 hours in Na||Na cells at -40 °C. In Na||Na2/3Ni1/4Cu1/12Mn2/3O2 full cells, it maintains a high capacity retention of 92.4% over 600 cycles with an initial specific capacity of 89.4 mAh g-1 at -40 °C, and achieves 81.7% capacity retention after 50 cycles with an initial specific capacity of 75.3 mAh g-1 at -78 °C. These results pave the way for the development of high-performance SMBs capable of operating under ultralow temperatures.

Sustainable Release of LiNO3 from a Fluorine‐Decorated Metal–Organic Framework Separator to Enable High‐Performance Li‐Metal Batteries in Carbonate Electrolytes

AbstractHigh‐voltage Li‐metal batteries hold great prospects for boosting energy density, while the Li‐metal anodes show poor compatibility with high‐voltage tolerant carbonate electrolytes, leading to unstable solid‐electrolyte interphase (SEI) and uncontrolled Li dendrites growth. Herein, a F‐decorated UIO‐66/polyimide (PI) functional separator encapsulated with LiNO3 (LNO@UIO‐66F/PI) is rationally designed to regulate the interfacial chemistry and Li deposition behavior. Specifically, the UIO‐66F nanoparticles in situ grown on the PI fibers form continuous electronegative nanochannels, which promote rapid and uniform Li+ flux while repelling the anion migration. Furthermore, the LiNO3 encapsulated in the UIO‐66F nanopores sustainably releases to form a thin and conductive Li3N‐rich SEI. This synergy effect induces a dense and spherical Li deposition behavior, effectively inhibiting the growth of Li dendrites. Consequently, this LNO@UIO‐66F/PI separator demonstrates highly reversible Li plating/stripping over 1000 h at an extremely high current density of 10 mA cm−2 in carbonate electrolytes, and also enables the stable cycling of Li||LiNi0.8Co0.1Mn0.1O2 cell over 1000 cycles under a high cut‐off voltage of 4.5 V, paving the way for practical application of high‐energy‐density Li‐metal batteries.

Electrolyte Chemistry Towards Ultra‐High Voltage (4.7 V) And Ultra‐Wide Temperature (−30 to 70 °C) LiCoO2 Batteries

AbstractLiCoO2 batteries for 3 C electronics demand high charging voltage and wide operating temperature range, which are virtually impossible for existing electrolytes due to aggravated interfacial parasitic reactions and sluggish kinetics. Herein, we report an electrolyte design strategy based on a partially fluorinated ester solvent (i.e., DFEA) that achieves a balance between weak Li+‐solvent interactions, sufficient salt dissociation, high interfacial stability, and superior thermal stability to address the aforementioned challenges. The resulting high‐voltage wide‐temperature electrolyte (HWE) not only possesses low desolvation energy, fast Li+ transport, high oxidation stability, excellent thermal‐abuse tolerance and non‐flammability, but also enables the formation of both inorganic‐rich cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI). Owing to the above merits, this HWE endows the highly stable operation of LiCoO2 cathodes under an ultra‐high voltage of 4.7 V and Graphite || LiCoO2 batteries in an ultra‐wide temperature range of −30 to 70 °C. Meanwhile, a 1.7 Ah‐level 4.6 V Graphite || LiCoO2 pouch cell with a high energy density of 240 Wh kg−1 also delivers excellent cycling stability, representing a significant advancement in the design of electrolytes towards ultra‐high voltage and ultra‐wide temperature batteries.

Revealing the Principles of Confining Electroplated Lithium beneath the CVD Grown Single Layer 2D Materials.

Owing to the nanoscale thickness, excellent mechanical and chemical stabilities, 2D materials including graphene and hexagonal boron nitride have emerged as promising artificial solid electrolyte interphase (SEI) candidates for lithium metal batteries. However, whether the implementation of 2D materials is beneficial to electrochemical performance remains controversial, and the key to confining the electroplated Li beneath the 2D materials remains elusive. Here, a nanocrystalline graphene (NG) film is synthesized on high-carbon Cu and the Li plating/stripping behavior on Cu grown with different 2D materials is investigated. Interestingly, in contrast to the commonly obtained Li particles on other substrates during nucleation, a smooth Li layer is obtained on NG/Cu, leading to a compact Li layer with more stable electrochemical performance. The finite element method simulations validate that the low electrical conductivity and the high density of defects on NG film drive the fast entry of electrolytes into the NG/Cu interface and promote homogenous Li nucleation. This work reveals the principles of confining electroplated Li beneath the 2D materials, and paves the way for the applications of 2D materials in artificial SEIs and anode-free lithium metal batteries.

A Thermally Robust Biopolymeric Separator Conveys K+ Transport and Interfacial Chemistry for Longevous Potassium Metal Batteries.

Potassium metal batteries (KMBs) hold promise for stationary energy storage with certain cost and resource merits. Nevertheless, their practicability is greatly handicapped by dendrite-related anodes, and the target design of specialized separators to boost anode safety is in its nascent stage. Here, we develop a thermally robust biopolymeric separator customized via a solvent-exchange and amino-siloxane decoration strategy to render durable and safe KMBs. Through experimental investigation and theoretical computation, we reveal that the optimized porosity and surface functionalization could manage ion transport and interfacial chemistry, thereby enabling efficient K+ diffusion and a favorable solid electrolyte interphase to achieve prolonged cycling stability (over 3000 h). The thus-assembled full cell retains 80% of its initial capacity after 400 cycles at 0.5 A g-1. The heat-proof property of the designed separator is further demonstrated. Our biopolymeric separator, affording multifunctional features, provides an appealing solution to circumvent instability and safety issues associated with potassium metal batteries.

Rational Electrolyte Design for Elevated-Temperature and Thermally Stable Lithium-Ion Batteries with Nickel-Rich Cathodes.

As the energy density of lithium-ion batteries (LIBs) increases, the shortened cycle life and the increased safety hazards of LIBs are drawing increasing concerns. To address such challenges, a series of localized high-concentration electrolytes (LHCEs) based on a solvating-solvent mixture of tetramethylene sulfone and trimethyl phosphate and a high flash-point diluent 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether were designed. The LHCEs exhibited nonflammability and greatly suppressed heat release at elevated temperatures, which would potentially improve the safety performance of the LIBs. Moreover, the optimal LHCE achieved capacity retentions of 87.1% and 81.7% in graphite||LiNi0.8Mn0.1Co0.1O2 cells after 500 cycles at 25 and 45 °C, respectively, which were significantly higher than the conventional electrolyte, whose capacity retentions were only 75.2% and 38.5% under the same conditions. Mechanistic studies revealed that the LHCE not only formed a more robust solid electrolyte interphase but also exhibited improved anodic stability, compared with the conventional electrolyte. This work sheds light on rational electrolyte design for high-energy density LIBs with high battery performance and low safety concerns.

A Bifunctional Imidazolyl Iodide Mediator of Electrolyte Boosts Cathode Kinetics and Anode Stability Towards Low Overpotential and Long-Life Li-O2 Batteries.

The addition of a redox mediator as soluble catalyst into electrolyte can effectively overcome the bottlenecks of poor energy efficiency and limited cyclability for Li-O2 batteries caused by passivation of insulating discharge products and unfavorable byproducts. Herein we report a novel soluble catalyst of bifunctional imidazolyl iodide salt additive, 1,3-dimethylimidazolium iodide (DMII), to successfully construct highly efficient and durable Li-O2 batteries. The anion I- can effectively promote the charge transport of Li2O2 and accelerate the redox kinetics of oxygen reduction/oxygen evolution reactions on the cathode side, thereby significantly decreasing the charge/discharge overpotential. Simultaneously, the cation DMI+ forms an ultrathin stably solid-electrolyte interphase film on Li metal, greatly inhibiting the shuttle effect of I- and improving the stability of anode. Using this DMII additive, our Li-O2 batteries achieve an extremely low voltage of 0.52 V and ultra-long cycling stability over 960 h. Notably, up to 95.8 % of the Li2O2 yield further proves the reversible generation/decomposition of Li2O2 without the occurrence of side reactions. Both experimental and theoretical results disclose that DMII enables Li+ easily solvated, testifying the dominance of the solution-induced reaction mechanism. This work provides the possibility to design the soluble catalysts towards high-performance Li-O2 batteries.

Transforming Detrimental Crystalline Zinc Hydroxide Sulfate to Homogeneous Fluorinated Amorphous Solid-Electrolyte Interphase on Zinc Anode.

The formation of non-ion conducting byproducts on zinc anode is notoriously detrimental to aqueous zinc-ion batteries (AZIBs). Herein, we successfully transform a representative detrimental byproduct, crystalline zinc hydroxide sulfate (ZHS) to fast-ion conducting solid-electrolyte interphase (SEI) via amorphization and fluorination induced by suspending CaF2 nanoparticles in dilute sulfate electrolytes. Distinct from widely reported nonhomogeneous organic-inorganic hybrid SEIs that exhibit structural and chemical instability, the designed single-phase SEI is homogeneous, mechanically robust, and chemically stable. These characteristics of the SEI facilitate the prevention of zinc dendrite growth and reduction of capacity loss during long-term cycling. Importantly, AZIB full cells based on this SEI-forming electrolyte exhibit exceptional stability over 20,000 cycles at 3 A/g with a charging voltage of 2.2 V without short circuits and electrolyte dry-out. This work suggests avenues for designing SEIs on a metal anode and provides insights into associated SEI chemistry.

Recent Advances on Characterization Techniques for the Composition-Structure-Property Relationships of Solid Electrolyte Interphase.

The Solid Electrolyte Interphase (SEI) is a nanoscale thickness passivation layer that forms as a product of electrolyte decomposition through a combination of chemical and electrochemical reactions in the cell and evolves over time with charge/discharge cycling. The formation and stability of SEI directly determine the fundamental properties of the battery such as first coulombic efficiency (FCE), energy/power density, storage life, cycle life, and safety. The dynamic nature of SEI along with the presence of spatially inhomogeneous organic and inorganic components in SEI encompassing crystalline, amorphous, and polymeric nature distributed across the electrolyte to the electrolyte-electrode interface, highlights the need for advanced in situ/operando techniques to understand the formation and structure of these materials in creating a stable interface in real-world operating conditions. This perspective discusses the recent developments in interface-sensitive in situ/operando techniques, providing valuable insights and addressing the challenges of understanding the composition/structure/property of SEI and their correlations during the formation processes at spatio-temporal resolution across various length scales.

Chemo‐Mechanics Interplay Dictates Interface Instability and Asymmetry in Plating and Stripping of Sodium Metal Electrodes

AbstractThe development of practical sodium (Na) metal batteries is hindered by key challenges including dendrite growth, dead metal formation, and unstable solid electrolyte interphase (SEI) growth. A fundamental understanding of the chemo‐mechanical interactions at the Na/SEI interface is critical for designing stable Na metal electrodes. In this work, the coupled electrochemical‐mechanical processes governing the morphological evolution and stability of Na metal during plating and stripping are investigated. The heterogeneous nature of transport and morphological interactions at the Na/SEI interface is revealed to result in nonuniform mechanical overpotentials and reaction fronts, eventually leading to Na filaments or pits. The spatio‐temporal evolution of stress heterogeneities during Na plating and stripping is shown to be asymmetric, manifesting in varying morphological nonuniformities and instability modes. The crucial role of external pressure in modulating the electrochemical‐transport interactions, the mechanical response of Na, and the localized reaction currents and stresses at the Na/SEI interface is demonstrated. At different external pressure conditions, the correlation between transport heterogeneities in the SEI and the onset and propagation of interface instability has been delineated. This work highlights the need for synergistic tailoring of external pressure and SEI heterogeneity toward achieving stable electrodeposition and dissolution in Na metal electrodes.

Sub‐Nano Confinement Engineering Toward Anion‐Reinforced Solvation Structure to Achieve Highly Reversible Anode‐Free Lithium Metal Batteries

AbstractThe practical application of anode‐free lithium metal batteries (AFLMBs) is impeded by poor cycling performance due to sluggish Li+ transport kinetics, unfavorable side reactions, and dendrite Li growth. To address these issues, ≈200 nm zeolitic imidazolate framework‐8 (ZIF‐8) interphase layer is introduced to enable highly reversible Li plating/stripping by electrosynthesis method. ZIF‐8 interphase layer with sub‐nano windows accelerates Li+ desolvation kinetics and thus suppresses unfavorable side reactions. Further, the internal cavities of ZIF‐8 serve as an anion reservoir to modulate anion‐reinforced solvation structure of Li+, facilitating the formation of LiF‐ and Li3N‐riched solid–electrolyte interphase. Thus, the Li/Cu@ZIF‐8 asymmetric cell exhibits remarkable Aurbach coulombic efficiency of 99.84%, and Cu@ZIF‐8/LiFePO4 AFLMB delivers impressive capacity retention (57.8%) over 400 cycles. This work highlights the effectiveness of ZIF‐8 to enable highly reversible AFLMBs and inspires the potential application of porous materials with sub‐nano windows and interval cavities in anode‐free batteries.

The Resurging of Hydrocarbon Gas as Early Sign of Battery Rollover Degradation.

Gas analysis offers real-time critical insights into the various processes occurring within batteries. However, monitoring battery degradation through gas formation remains relatively underexplored. Traditional coin cell setups pose challenges for long-cycle experiments and do not accurately reflect real-life battery usage. In this study, online electrochemical mass spectrometry (OEMS) was used to monitor gas evolution in a 4500 mAh NMC/graphite 21700 cylindrical battery throughout its cycling life. By tracking gas species and quantities, we identified distinct phases of gas evolution corresponding to different stages of degradation. Notably, the resurgence of hydrocarbon gases such as C2H4 emerged as an early indicator of rollover degradation. Furthermore, the continuous dissolution and reformation of the solid-electrolyte interphase (SEI) layer was identified as the primary driver of battery degradation. This study demonstrates the potential for integrating miniature gas sensors into battery systems for real-time health monitoring and early degradation detection.

Bilayer Artificial Solid Electrolyte Interphase with 75 GPa Young's Modulus Enable High Energy Density Lithium Metal Pouch Cells

Bilayer Artificial Solid Electrolyte Interphase with 75 GPa Young's Modulus Enable High Energy Density Lithium Metal Pouch Cells

Competitive Coordination and Dual Interphase Regulation of MOF-Modified Solid-State Polymer Electrolytes for High-Performance Sodium Metal Batteries.

Solid-state polymer electrolytes (SPEs) have emerged as prominent candidates for solid-state sodium metal batteries (SMBs) due to their enhanced flexibility and reduced interfacial resistance. However, their performance is limited by poor Na+ conductivity at room temperature, disordered ion transport properties and unstable interfaces. Herein, a three-dimensional (3D) interconnected copper metal organic framework (Cu-MOF) on polyacrylonitrile (PAN) fibers is introduced into polyethylene oxide (PEO)-based SPEs to construct a composite electrolyte (PPNM). The open metal sites (OMS) of the Cu-MOF compete with Na+, effectively coordinating with TFSI- anions and oxygen atoms in PEO, thereby reducing concentration polarization, weakening the Na+-O binding strength and facilitating Na+ migration. By harnessing the multifunctional properties of Cu-MOF and PAN, the PPNM electrolyte exhibits superior ionic conductivity (1.03×10-4 S cm-1) and a high Na+ transference number (0.58) at room temperature. The strong anchoring of TFSI- anions by Cu-MOF promotes the formation of inorganic-rich (NaF and Na3N) cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) layers, enhancing dual interfacial stability. The Na3V2(PO4)3@C/PPNM/Na full cells realize robust cycling performance for 2000 cycles at 200 mA g-1. This work provides a facile strategy for regulating the Na+ coordination state and interphase engineering in solid-state SMBs.

Key Anodic Interfacial Phenomena and their Control in Next-Generation Lithium and Sodium Metal Batteries.

Advancing next-generation battery technologies requires a thorough understanding of the intricate phenomena occurring at anodic interfaces. This focused review explores key interfacial processes, examining their thermodynamics and consequences in ion transport and charge transfer kinetics. It begins with a discussion on the formation of the electro chemical double layer, based on the GuoyChapman model, and explores how charge carriers achieve equilibrium at the interface. This review then delves into essential interfacial processes, including metal nucleation and growth, the development and stability of the solid electrolyte interphase (SEI), and ion movement across the interface. In addition, it analyzes the impact of different electrolyte solutions-such as low- and high-concentration electrolytes and localized high-concentration electrolytes-on these interfacial processes. The role of additives, co-solvents, and diluents in modifying these interfaces is also covered. This review further evaluates techniques for characterizing the SEI layer, highlighting their strengths and limitations in both aqueous and nonaqueous battery systems. By comparing the challenges and opportunities associated with interfaces next-generation nonaqueous metal battery systems, this review aims to offer new insights into their respective advantages and limitations, ultimately guiding the design and optimization of anodic interfaces to enhance the safety and efficiency of future energy storage technologies.

Structural Design and Challenges of Micron-Scale Silicon-Based Lithium-ion Batteries.

Currently, lithium-ion batteries (LIBs) are at the forefront of energy storage technologies. Silicon-based anodes, with their high capacity and low cost, present a promising alternative to traditional graphite anodes in LIBs, offering the potential for substantial improvements in energy density. However, the significant volumetric changes that silicon-based anodes undergo during charge and discharge cycles can lead to structural degradation. Furthermore, the formation of excessive solid-electrolyte interphases (SEIs) during cycling impedes the efficient migration of ions and electrons. This comprehensive review focuses on the structural design and optimization of micron-scale silicon-based anodes from both materials and systems perspectives. Significant progress is made in the development of advanced electrolytes, binders, and conductive additives that complement micron-scale silicon-based anodes in both half and full-cells. Moreover, advancements in system-level technologies, such as pre-lithiation techniques to mitigate irreversible Li+ loss, have enhanced the energy density and lifespan of micron-scale silicon-based full cells. This review concludes with a detailed classification of the underlying mechanisms, providing a comprehensive summary to guide the development of high-energy-density devices. It also offers strategic insights to address the challenges associated with the large-scale deployment of silicon-based LIBs.