Electrolyte Decomposition Research Articles

Achievable dual-strategy to stabilize Li-rich layered oxide interface by a one-step wet chemical reaction towards long oxygen redox reversibility

Oxygen release and electrolyte decomposition under high voltage endlessly exacerbate interfacial ramifications and structural degradation of high energy-density Li-rich layered oxide (LLO), leading to voltage and capacity fading. Herein, the dual-strategy of CrxB complex coating and local gradient doping is simultaneously achieved on LLO surface by a one-step wet chemical reaction at room temperature. Density functional theory (DFT) calculations prove that stable B–O and Cr–O bonds through the local gradient doping can significantly reduce the high-energy O 2p states of interfacial lattice O, which is also effective for the near-surface lattice O, thus greatly stabilizing the LLO surface. Besides, differential electrochemical mass spectrometry (DEMS) indicates that the CrxB complex coating can adequately inhibit oxygen release and prevents the migration or dissolution of transition metal ions, including allowing speedy Li+ migration. The voltage and capacity fading of the modified cathode (LLO-CrB) are adequately suppressed, which are benefited from the uniformly dense cathode electrolyte interface (CEI) composed of balanced organic/inorganic composition. Therefore, the specific capacity of LLO-CrB after 200 cycles at 1C is 209.3 mA h g–1 (with a retention rate of 95.1%). This dual-strategy through a one-step wet chemical reaction is expected to be applied in the design and development of other anionic redox cathode materials.

Lithium p-toluenesulfinate-coated poly(imide) separators for enhanced safety and electrochemical performances of lithium-ion batteries

Increasing the energy density of lithium-ion batteries enhances their applicability; however, ensuring their safety remains a critical issue in the energy society. Herein, we report the development of a lithium p-toluenesulfinate (PTSL)-coated polyimide (PI) separator with improved safety and electrochemical performance during cycling. It is anticipated that integrating PTSL particles into the PI separator will mitigate the risk of internal short circuits by clogging the porous structure of the PI separator and enhance the interfacial stability of the electrode materials. The PTSL is expected to act as an effective component of protective layers, physically separating the cathode from direct contact with electrolytes. The PTSL-embedded PI separator regulated the porous structure inherent to the PI separator, thereby enhancing its physical and thermal properties, such as improved wetting characteristics (evidenced by higher ionic conductivities and lithium-ion transference numbers) and thermal behaviors (reduced shrinkage and more stable thermal decomposition behaviors). During cycling, the cells with the PTSL-coated PI separator demonstrated increased cycling retention compared to the cells with graphite/NCM811 electrodes because the additional PTSL-based protective layers mitigated the electrolyte decomposition upon cycling.

Quantification of solvent-mediated host-ion interaction in graphite intercalation compounds for extreme-condition Li-ion batteries

Achieving simultaneous fast-charging capabilities and low-temperature adaptability in graphite-based lithium-ion batteries (LIBs) with an acceptable cycle life remains challenging. Herein, an ether-based electrolyte with temperature-adaptive Li+ solvation structure is designed for graphite, and stable Li+/solvent co-intercalation has been achieved at subzero. As revealed by in-situ variable temperature (−20 ℃) X-ray diffraction (XRD), the poor compatibility of graphite in ether-based electrolyte at 25 ℃ is mainly due to the continuous electrolyte decomposition and the in-plane rearrangement below 0.5 V. Former results in a significant irreversible capacity, while latter maintains graphite in a prolonged state of extreme expansion, ultimately leading to its exfoliation and failure. In contrast, low temperature triggers the rearrangement of Li+ solvation structure with stronger Li+/solvent binding energy and shorter Li+–O bond length, which is conducive for reversible Li+/solvent co-intercalation and reducing the time of graphite in an extreme expansion state. In addition, the co-intercalation of solvents minimizes the interaction between Li-ions and host graphite, endowing graphite with fast diffusion kinetics. As expected, the graphite anode delivers about 84% of the capacity at room temperature at −20 ℃. Moreover, within 6 min, about 83%, 73%, and 43% of the capacity could be charged at 25, −20, and −40 ℃, respectively.

Fluorinated solid electrolyte interphase enables interfacial stability for sulfide-based solid-state sodium metal batteries

Sulfide solid electrolytes (SSEs) with high ionic conductivity and good mechanical flexibility are considered ideal for all-solid-state sodium metal batteries (ASSSMBs). Nevertheless, the detrimental interfacial issue between SSEs and Na metal presents a significant challenge for sulfide-based ASSSMBs. Herein, we demonstrate a facile and cost-effective method for constructing a controllable NaF-rich artificial interphase on the surface of sodium metal anodes by incorporating perfluoropolyether (PFPE). A stratified solid electrolyte interphase (SEI) composed a nanocrystalline NaF inner phase and organic outer shell, efficaciously seals the Na surface. The interfacial interactions between SSEs and Na metal is explored using Comsol and ab initio molecular dynamics simulations, revealing that the presence of a NaF-rich artificial interphase hinders the growth of sodium dendrites and mitigates the decomposition of the sulfide electrolytes. As a result, the symmetric cell exhibits stable Na plating/stripping cycling for 800 h at 0.1 mA cm−2. Overall, our PFPE-modified sodium metal anodes offer a promising avenue for the widespread application of high-performance ASSSMBs.

Facile self-assembled monolayer deposition on copper foil for high-performance lithium-metal batteries

Li metal is widely acknowledged as the optimal negative electrode material for high-energy-density Li rechargeable batteries. However, challenges arise owing to the formation of Li dendrites and poor surface stability, leading to reduced cycle life and energy efficiency, thereby limiting widespread application. In this study, we introduced a novel approach of a molecular single-layer surface modification onto a Cu foil using a self-assembled monolayer with hexamethyldisilane (HMDS) to enhance the performance of Li-metal electrodes. The deposition of a single molecular layer at the Å-level was achieved by a simple combination of precursor casting and heat treatment without greatly affecting the energy and power density. Furthermore, this process was both scalable and cost-effective, making it highly suitable for large-scale battery manufacturing. The molecular deposition of HMDS effectively mitigated electrolyte decomposition and promoted uniform Li deposition by enhancing the surface stability under repeated Li plating–stripping processes. Optical microscopy revealed the homogeneous Li plating even after extended cycling; the first cycle on the modified surface depicted uniform plating without blank spots owing to the reduced gas-phase by-products from electrolyte decomposition. Thus, HMDS modification greatly improved the cycle stability of Li-metal batteries by successfully mitigating polarization due to electrolyte decomposition. Such improvement improved the Coulombic efficiencies and enhanced the energy efficiency, especially over a wide current density range of 1–5 mA cm−2. Furthermore, full cells with LiFePO4 cathodes and HMDS-modified Cu foils exhibited extended cyclability with increased energy efficiencies.

Low LUMO energy carbon molecular interface to suppress electrolyte decomposition for fast charging natural graphite anode

Graphite holds great potential as a next-generation anode material for energy storage devices. However, the low working voltage of graphite leads to electrolyte decomposition, generating harmful byproducts like HF, while its anisotropic structure results in poor Li+ transport kinetics, making it challenging to balance battery stability and fast-charging performance. Herein, a controllable and scalable carbon molecular layer with low-LUMO (lowest unoccupied molecular orbital)energy is successfully designed to alter charge transfer at the electrode surface. The low LUMO energy carbon molecular interlayer between the graphite and solid electrolyte interphase (SEI) contains numerous strong electron-withdrawing and polar functional groups (C-F and C-N). The functional groups in the interlayer can preferentially and rapidly convert into a LiF and Li3N-rich SEI, attributed to their lower reaction energy barrier compared to electrolyte decomposition. Importantly, the electronic effects and intramolecular synergistic effects between polar functional groups make the conversion of C-F to LiF easier. The interayer superior properties that prevent SEI acid corrosion, accelerates the Li+ desolvation and diffusion in the SEI. Therefore, the graphite anode achieves a balance between fast charging and stability, retaining 64.28 % capacity retention after 1000 cycles at 10 A g−1. Additionally, the graphite anode can be applied in potassium-ion batteries, achieving 148.3 mAh g−1 at 0.2 A g−1. This simple and effective interfacial molecular design offers new insights for simultaneously regulating SEI and suppress electrolyte decomposition.

Quantifying the Aging of Lithium-Ion Pouch Cells Using Pressure Sensors

Understanding the behavior of pressure increases in lithium-ion (Li-ion) cells is essential for prolonging the lifespan of Li-ion battery cells and minimizing the safety risks associated with cell aging. This work investigates the effects of C-rates and temperature on pressure behavior in commercial lithium cobalt oxide (LCO)/graphite pouch cells. The battery is volumetrically constrained, and the mechanical pressure response is measured using a force gauge as the battery is cycled. The effect of the C-rate (1C, 2C, and 3C) and ambient temperature (10 °C, 25 °C, and 40 °C) on the increase in battery pressure is investigated. By analyzing the change in the minimum, maximum, and pressure difference per cycle, we identify and discuss the effects of different factors (i.e., SEI layer damage, electrolyte decomposition, lithium plating) on the pressure behavior. Operating at high C-rates or low temperatures rapidly increases the residual pressure as the battery is cycled. The results suggest that lithium plating is predominantly responsible for battery expansion and pressure increase during the cycle aging of Li-ion cells rather than electrolyte decomposition. Electrochemical impedance spectroscopy (EIS) measurements can support our conclusions. Postmortem analysis of the aged cells was performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to confirm the occurrence of lithium plating and film growth on the anodes of the aged cells. This study demonstrates that pressure measurements can provide insights into the aging mechanisms of Li-ion batteries and can be used as a reliable predictor of battery degradation.

Artificially regulated interphase on natural graphite realizes rapid charge and durable high-temperature cycling of Li-ion batteries

Natural graphite (NG) is a strong competitor in the anode market of Li-ion batteries because of its low cost, rich resource, low energy consumption and low carbon dioxide emission during production. The main problems inhibiting its universal application are its high surface area and the attendant unstable solid/electrolyte interphase (SEI), leading to unsatisfactory cycling and rate performance. In this work, a Li+-conductive, thermally and mechanically stable organic polymer layer is successfully constructed on NG surface by virtue of the simultaneous polymerization and crosslinking reactions of chitosan (CS) and acrylic acid (AA). With controllable thickness, the polymer layer denoted as CSAA significantly decreases the specific surface area of NG, works as an inner SEI substrate greatly mitigating the decomposition of electrolyte, and induces the formation of a LiF-rich SEI outer layer. The SEI resistance and activation energy for charge-transfer reactions are considerably reduced. Benefiting from the superior properties of CSAA-derived SEI, the NG@CSAA anodes exhibit a high initial coulombic efficiency of 94.1 %, fast charge/discharge capability and prolonged cycle life at both 25 °C and 45 °C in the LiFePO4 cathodes-based full cells.

Overlooked challenges of interfacial chemistry upon developing high energy density silicon anodes for lithium-ion batteries

Evaluation of silicon (Si) anode performance by the assembled Si||Li half-cells is the primary approach in the development of high-energy-density lithium-ion batteries (LIBs). However, most studies focus solely on the variations of Si anode, the stability of electrolyte on the lithium (Li)-metal counter electrode has been overlooked. Herein, we discovered that the acquired cell performance not only depends on the Li+ (de-)solvation behaviors on the Si anode surface but also was affected significantly by the lithiation overpotential caused by the side reactions on the Li electrode. It is significant to identify this point, as these influences of electrolyte decomposition on the Li electrode have been previously regarded as an integral part of side reactions on the Si anode. We proposed a new perspective of the electrolyte solvation structure and electrode interfacial model to unravel the interfacial behaviors on the Si and Li electrodes respectively. The identified differences in the Li+ solvation and (de-)solvation behaviors not only provide reasons for the varied electrolyte stability in different electrolytes but also interpret the superior performance in tetrahydrofuran (THF)-based electrolytes. This study underscores the importance of understanding electrolyte behavior at the interfaces of individual electrodes to discern the reliability of electrode performance and also introduce a novel principle for designing superior electrolytes for high-energy-density LIBs.

Unravelling the anionic stability of an ether-based electrolyte with a hard carbon or metallic sodium anode for high-performance sodium-ion batteries

In hard carbon (HC) anodes, elucidating the relationship between the solid electrolyte interphase formation and the solvated Na+ co-intercalation mechanism is crucial, particularly considering different anionic salts in ether-based electrolytes. Here, we comprehensively explore the impact of different anionic salts on the electrochemical performance of HC/Na half-cell and elucidate the underlying mechanism through experimental studies and theoretical calculations. The surface morphology of the HC anode and its interphasial property are further investigated to evaluate the differences endowed by the presence of various anionic salts in diglyme (2G). The HC/Na half-cells with NaPF6-2G and sodium trifluoromethanesulfonate (NaCF3SO3)-2G display superior electrochemical performance with faster kinetics and lower interfacial resistance than those with NaClO4-2G, sodium bis-(fluorosulfonyl) imide (NaFSI)-2G and sodium bis-(trifluoromethanesulfonyl) imide (NaTFSI)-2G. NaClO4-2G forms a relatively thick interphase layer with high resistance at the electrode/electrolyte interface owing to its insufficient stability. NaFSI-2G and NaTFSI-2G exhibit severe side reactions with Na metal, producing a thick interphase layer on the HC surface with high interfacial resistance from excess electrolyte decomposition, thus deteriorating the electrochemical performance. In summary, the study on the stability of different anionic salts in ether-based electrolyte for the HC anode with the intercalation mechanism provides valuable insights for screening appropriate conductive salts for high-performance sodium-ion batteries, especially when considering Na metal counter/reference electrodes.

Waste polyethylene terephthalate-derived organic-inorganic hybrid materials as sustainable dual electrodes for Li-ion batteries

The hybrid Fe-Li2TP structure is constructed from waste polyethylene terephthalate (w-PET) derived dilithium terephthalate (Li2TP) and conventional Fe2O3 by hydrothermal reaction. It is being studied for both anode and cathode for LIBs. As an anode, it exhibits a reversible capacity of 505 mAh/g after 100th cycle at 1 C-rate with ∼100 % coulombic efficiency (CE). In addition, as a cathode, it shows highly reversible charge/discharge capacities of 107.50/107.52 mAh/g after the 100th cycle at 0.1 C-rate with 100 % CE. Further, in the cathodic studies via galvanostatic intermittent titration technique (GITT), the average lithium diffusion (DLi+) coefficients are calculated to be 2.96 × 10-10, 3.89 × 10−10 cm2 s−1 and the electrical (µ) mobilities to be 5.86 × 1011 m2 V−1 s−1, 1.12 × 1011 m2 V−1 s−1 for charge and discharge pulses, respectively. The combined nano-rod and nano-spherical morphologies reduce the diffusion length, and adding 10 % SWCNTs during electrode fabrication enhances the electronic conductivity. This organic–inorganic hybrid strategy of Fe-Li2TP strongly mitigates the electrode dissolution, reducing the structural strain and preventing electrolyte decomposition at higher voltage. Computational studies show an optimized Fe-Li2TP structure with a 2.7-fold lower band gap value (1.9040 eV) than the pristine Li2TP.

Adsorptive Shield Derived Cathode Electrolyte Interphase Formation with Impregnation on LiNi0.8Mn0.1Co0.1O2 Cathode: A Mechanism-Guiding-Experiment Study.

Lithium difluoro(oxalate) borate (LiDFOB) contributes actively to cathode-electrolyte interface (CEI) formation, particularly safeguarding high-voltage cathode materials. However, LiNixCozMnyO2-based batteries benefit from the LiDFOB and its derived CEI only with appropriate electrolyte design while a comprehensive understanding of the underlying interfacial mechanisms remains limited, which makes the rational design challenging. By performing ab initio calculations, the CEI evolution on the LiNi0.8Co0.1Mn0.1O2 has been investigated. The findings demonstrate that LiDFOB readily adheres to the cathode via semidissociative configuration, which elevates the Li deintercalation voltage and remains stable in solvent. Electrochemical processes are responsible for the subsequent cleavage of B-F and B-O bonds, while the B-F bond cleavage leading to LiF formation is dominant in the presence of adequate Li+ with a substantial Li intercalation energy. Thus, impregnation is established as an effective method to regulate the conversion channel for efficient CEI formation, which not only safeguards the cathode's structure but also counters electrolyte decomposition. Consequently, in comparison to utilizing LiDFOB as an electrolyte additive, employing LiDFOB impregnation in the NCM811/Li cell yields significantly improved cycling stability for over 2000 h.

Enhancing electric field intensity of interfacial electric double layer to improve properties of solid electrolyte interface for sodium-ion batteries

The electrical double layer (EDL) provides a critical area, where the specific adsorption on the electrode dominates the initial structure and chemical composition of the solid electrolyte interface (SEI) film. Therefore, the SEI can be optimized by adjusting the properties of the EDL. Here, we regulate the properties of EDL to optimize the composition and morphology of the SEI film on the hard carbon anode surface by adding NaF with small molecule structure. The preferential accumulation of NaF additives on the electrode surface enhances the electric field intensity and promotes electrolyte decomposition. That is, the formed SEI film rich in inorganic NaF and B-O components, can significantly improve the storage capacity of sodium ions in the hard carbon anode and accelerate the rapid transport of sodium ions. This strategy enables the cycling capacity to improve by 13.5 %, and maintain a stable capacity retention rate of 86.2 % at the rate of 1C after 500 cycles, thereby extending the lifespan and increasing the capacity of the rechargeable battery. The strategy that utilizing small molecule additives to enhance the electric field intensity of EDL provides a new approach to improve the performances of SEI film and battery performances.

LiF/ LixPOy/ LixPOyFz-based artificial interface on graphitic cathode for improving the cycle life of dual ion batteries

The emerging dual-ion batteries are a sustainable analog of conventional Lithium-ion batteries. It yields high voltage output and satisfying capacity, replacing transition metal-based cathodes with graphitic carbon. Despite the advantages, the systems suffer from inadequate cycling efficiencies and triggered electrolyte decomposition on cathode surface that cut short the cycle life. As a protective measure, the carbon cathode is coated using a LiF/LixPOy/LixPOyFz-based hybrid coating layer derived from the thermal decomposition of LiPF6 salt. The coated layer acts as an artificial interface that safeguards the surface from electrolyte attack and enhances cycling efficiencies. It forms a mechanochemically robust cathode-electrolyte interface that preserves the graphitic order and structural integrity of the electrode. As a result, the bulk of the coated material is not ruptured like in the uncoated pristine sample, thereby assisting in long-term cycling. The coated material retains 85 % capacity even after 1000 cycles with a 10 % improved coulombic efficiency and 130 mV reduced voltage hysteresis instead of losing 15 % capacity within 50 cycles with poor efficiency and elevated resistances in the pristine material. The strategy brings fruitful outcomes when applied in dual carbon cell and is believed to be equally effective in other dual-ion systems.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Multifunctional fluorinated phosphonate-based localized high concentration electrolytes for safer and high-performance lithium-based batteries

This study introduces a novel fluorinated phosphonate-based additive, Bis(2,2,2-trifluoroethyl)(methoxycarbonylmethyl)phosphonate (BTCMP), in a localized high-concentration electrolyte (LHCE) to address key challenges in lithium metal batteries (LMBs), such as dendritic lithium growth and porous electrode morphology. The pristine LHCE forms a fluorine-rich solid electrolyte interphase (SEI) layer, primarily composed of lithium fluoride (LiF). However, the pristine LHCE suffers from severe electrolyte decomposition, forming a thicker and more resistive cathode electrolyte interphase (CEI), leading to increased impedance and reduced cyclability. Interestingly, Density Functional Theory (DFT) investigations revealed that the BTCMP inclusion modifies the solvation structure by dispersing the aggregates into smaller fragments, facilitating easier Li+ migration than the pristine LHCE. The addition of BTCMP suppresses solvent decomposition as confirmed by an increasing trend in the lowest unoccupied molecular orbital (LUMO) of corresponding LHCE molecules. Further, the presence of BTCMP results in a thinner and more stable CEI, reducing electrolyte decomposition, maintaining better ion transport, and preserving the cathode's structural integrity, as supported by TEM and XPS analysis. The BTCMP-based F-rich LHCE retained 82 % of its initial capacity while maintaining a coulombic efficiency of 99.5 % after 200 cycles in a Li||LNMO cell while the pristine LHCE only retained 47.2 % of initial capacity post-150 cycles. Additionally, the flame-retardant properties of BTCMP-based LHCE highlight its safety compared to commercial electrolytes.

Regulating Anode‐Electrolyte Interphasial Reactions by Zwitterionic Binder Chemistry in Lithium‐Ion Batteries with High‐Nickel Layered Oxide Cathodes and Silicon‐Graphite Anodes

AbstractThe practical application of silicon (Si)‐based anodes faces challenges due to severe structural and interphasial degradations. These challenges are exacerbated in lithium‐ion batteries (LIBs) employing Si‐based anodes with high‐nickel layered oxide cathodes, as significant transition‐metal crossover catalyzes serious parasitic side reactions, leading to faster cell failure. While enhancing the mechanical properties of polymer binders has been acknowledged as an effective means of improving solid‐electrolyte interphase (SEI) stability on Si‐based anodes, an in‐depth understanding of how the binder chemistry influences the SEI is lacking. Herein, a zwitterionic binder with an ability to manipulate the chemical composition and spatial distribution of the SEI layer is designed for Si‐based anodes. It is evidenced that the electrically charged microenvironment created by the zwitterionic species alters the solvation environment on the Si‐based anode, featuring rich anions and weakened Li+‐solvent interactions. Such a binder‐regulated solvation environment induces a thin, uniform, robust SEI on Si‐based anodes, which is found to be the key to withstanding transition‐metal deposition and minimizing their detrimental impact on catalyzing electrolyte decomposition and devitalizing bulk Si. As a result, albeit possessing comparable mechanical properties to those of commercial binders, the zwitterionic binder enables superior cycling performances in high‐energy‐density LIBs under demanding operating conditions.

In-situ Formation of a LiF-rich Interphase for Graphite Anode Operated at Low Temperatures.

Inorganic LiF is generally a desirable component in solid electrolyte interface (SEI) for graphite anode due to its electronic insulation, low Li+ diffusion barrier, high modulus and good chemical stability. Herein, fluorinated carbon (CFx) was incorporated into graphite material, which exhibited a high discharge potential prior to electrolyte decomposition and in-situ formed a crystalline LiF-based SEI with improved Li+ diffusion rate. The optimized graphite anode therefore demonstrated a fast-charging capability with 124 mAh g-1 at high rate of 8 C and a remarkable capacity retention of 83.8% at the low temperature of -30 oC compared to that at 25 oC. Furthermore, the optimized graphite|LiFePO4 full cell exhibited a significantly high discharge capacity of 109 mAh g-1 at -30 oC, corresponding to a notable 77.3% room-temperature capacity retention. These findings highlight a facile strategy to attain a LiF-rich SEI for high-performance lithium-ion batteries.

Probing microstructure evolution of Si/C anode for Li-ion batteries via synchrotron transmission X-ray tomographic microscopy

Holding great potentials as an excellent anode for Li-ion batteries, Si has received enormous attention, and its degradation theory has been enriched extensively based on various characterizations over time. To provide a more comprehensive diagnosis for current Si/C anodes, ex situ phase-contrast synchrotron transmission X-ray tomographic microscopy (TXTM) is applied to study a Si/C electrode sampled at representative cycling numbers. Through a series of data segmentations and identifications, three-dimensional Si/C electrodes are described in details with both global and localized structure features, which are rationally linked to the electrochemical characteristics as well as the previous discoveries. This successfully establishes an updated electrode-level failure process for common Si/C anodes where the electrode degradation is primarily initiated by the nonstop Si-phase pulverization with continually-expanded LixSi/electrolyte interface, and manifested as the internal void space expansion and the ever-growing electrode thickness. Bearing this in mind, multiple complementary and synergistic solutions towards limiting the intrinsic Si rupture and electrolyte decomposition should be developed to ensure a high-performance Si-based anode over long-term cycling for Li-ion battery in the near future.

Designing electrolytes for enhancing stability and performance of lithium-ion capacitors at large-scale cylindrical cells

This study investigates the impact of fluorinated ethylene carbonate (FEC) as a co-solvent in the electrolytes of large-scale lithium-ion capacitors (LICs), an area previously unexplored. Our comprehensive analysis integrates electrochemical analysis, gas detection, and surface chemical examination to assess the performance and stability of a 1.2 M LiPF6 electrolyte system. We explored various formulations, including a standard EC/EMC/DEC mixed solvent and newly designed electrolytes with FEC additions, such as EC/EMC/DEC/FEC and DMC/FEC blends. Our findings demonstrate that the DMC/FEC blend matches and even surpasses the capacity retention of traditional electrolytes, suggesting enhanced long-term stability. FEC's presence significantly reduces electrolyte decomposition, as confirmed by in situ Differential Electrochemical Mass Spectrometry and ex-situ gas chromatography. Further, surface chemical analysis highlighted the formation of a stable, LiF-rich solid electrolyte interface (SEI) when FEC is included, thereby improving the chemical stability of the system. These results underline FEC's crucial role in optimizing electrolyte compositions, thus advancing the development of more efficient and durable LIC systems. FEC's integration into LIC electrolytes represents a significant breakthrough, enhancing overall performance and longevity, with broad implications for the application of LICs in various technologies.