Search

Next‐generation Li‐ion batteries are expected to exhibit superior energy and power density, along with extended cycle life. Ni‐rich high‐capacity layered nickel manganese cobalt oxide electrode materials (NMC) hold promise in achieving these objectives, despite facing challenges such as capacity fade due to various degradation modes. Crack formation within NMC‐based cathode secondary particles, leading to parasitic reactions and the formation of inactive crystal structures, is a critical degradation mechanism. Mechanical and chemical degradation further deteriorate capacity and lifetime. To mitigate these issues, an artificial cathode electrolyte interphase can be applied to the active material before battery cycling. While atomic layer deposition (ALD) has been extensively explored for active material coatings, molecular layer deposition (MLD) offers a complementary approach. When combined with ALD, MLD enables the deposition of flexible hybrid coatings that can accommodate electrode material volume changes during battery operation. This study focuses on depositing TiO2‐titanium terephthalate thin films on a LiNi0.8Mn0.1Co0.1O2 electrode via ALD‐MLD. The electrochemical evaluation demonstrates favorable lithium‐ion kinetics and reduced electrolyte decomposition. Overall, the films deposited through ALD‐MLD exhibit promising features as flexible and protective coatings for high‐energy lithium‐ion battery electrodes, offering potential contributions to the enhancement of advanced battery technologies and supporting the growth of the EV and stationary battery industries. [ABSTRACT FROM AUTHOR]

This research elucidates novel insights into the electrochemical properties and degradation phenomena of propylene carbonate (PC)‐based supercapacitors at a large‐scale 18650 cylindrical jelly‐roll cell level. Central to our findings is the identification of 2‐ethyl‐4‐methyl‐1,3‐dioxolane (EMD) as a hitherto undocumented decomposition by‐product, highlighting the nuanced complexity of PC electrolyte stability. We further demonstrate that elevated operational voltages precipitate accelerated electrolyte degradation, underscoring the criticality of defining the operational voltage window for maximizing device longevity. Employing advanced analytical techniques, including gas chromatography‐mass spectrometry (GC‐MS), this study meticulously analyzes electrolyte decomposition mechanisms. The outcomes offer pivotal insights into the operational constraints and chemical resilience of PC‐based supercapacitors, contributing significantly to the optimization of supercapacitor design and application. By delineating a specific decomposition pathway, this investigation enriches the understanding of electrochemical dynamics in supercapacitor systems, providing a foundation for future research and technological advancement in energy storage devices. [ABSTRACT FROM AUTHOR]

Alleviating the decomposition of the electrolyte is of great significance to improving the cycle stability of cathodes, especially for LiCoO2 (LCO), its volumetric energy density can be effectively promoted by increasing the charge cutoff voltage to 4.6 V, thereby supporting the large‐scale application of clean energy. However, the rapid decomposition of the electrolyte under 4.6 V conditions not only loses the transport carrier for lithium ion, but also produces HF and insulators that destroy the interface of LCO and increase impedance. In this work, the decomposition of electrolyte is effectively suppressed by changing the adsorption force between LCO interface and EC. Density functional theory illustrates the LCO coated with lower electronegativity elements has a weaker adsorption force with the electrolyte, the adsorption energy between LCO@Mg and EC (0.49 eV) is weaker than that of LCO@Ti (0.73 eV). Meanwhile, based on the results of time of flight secondary ion mass spectrometry, conductivity‐atomic force microscopy, in situ differential electrochemical mass spectrometry, soft X‐ray absorption spectroscopy, and nuclear magnetic resonance, as the adsorption force increases, the electrolyte decomposes more seriously. This work provides a new perspective on the interaction between electrolyte and the interface of cathode and further improves the understanding of electrolyte decomposition. [ABSTRACT FROM AUTHOR]

The gas release within Li‐ion batteries, particularly during cycling and storage, can result in rapid performance degradation and potential safety hazards. However, this area has not garnered sufficient attention until now, primarily because the gassing information collected by typical OEMS/DEMS is quite limited and even inaccurate. Herein, for the first time, a state‐of‐the‐art on‐line GC‐BID/MS to full‐dimensionally analyze the gassing behavior within both lab‐scale coin‐type cell (in situ mode) and industry‐scale pouch‐type cell (operando mode) is originally designed/constructed. Not limited to common permanent gases (e.g. H2, CO, etc.) detected by online GC‐BID, but also complicated/various (semi‐)volatile products are identified/quantified by online GC‐MS. Based on the real‐time evolution information of water, alcohols, aldehydes, ethers, esters, and hydrocarbons, the decomposition mechanisms of electrolyte on both graphite anode and/or LCO cathode sides is further supplemented/perfected. Moreover, at the level of the device, series derivative/crosstalk reactions induced by trapped/accumulated gaseous species are unveiled in practical pouch‐cell. [ABSTRACT FROM AUTHOR]

[Display omitted] Pyrite FeS 2 , as a promising conversion-type cathode material, faces rapid capacity degradation due to challenges such as polysulfide shuttle and massive volume changes. Herein, a localized high-concentration electrolyte (LHCE) based on dual-salt lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) is designed to address the challenges. By the dual-salt strategy, we tailor a more desirable solvation structure than that in the single-salt system. Specifically, the solvation structure involving FSI− and TFSI− enables milder electrolyte decomposition, which reduces initial capacity loss. Meanwhile, it facilitates the formation of a stable and flexible cathode/electrolyte interphase (CEI), effectively mitigating side effects and accommodating volume changes. Consequently, the micro-sized FeS 2 realizes a capacity of 641 mAh g−1 after 600 cycles with a retention rate of 90%, significantly improving the cycling stability of the FeS 2 cathode. This work underscores the pivotal role of solvation structure in modulating electrochemical performances and provides a simple and effective electrolyte design concept for conversion-type cathodes. [ABSTRACT FROM AUTHOR]

Understanding the behavior of lithium-ion battery electrolytes during thermal runaway is essential for designing safer batteries. However, current reports on electrolyte decomposition behaviors often focus on reactions with electrode materials. Herein we use quantum chemical calculations to develop a model for the thermal decomposition mechanism of electrolytes under both electrolyte and ambient atmosphere conditions. The thermal stability is found to be associated with the dielectric constants of electrolyte constituents. Within the electrolyte, the solvation effects between molecules increase electrolyte stability, making thermal decomposition a more difficult process. Furthermore, Li+is observed to facilitate electrolyte thermal decomposition, as the energy required for the thermal decomposition reactions of molecules decreases when they are bonded with Li+. It is hoped that this study will offer a theoretical basis for understanding the complex reactions occurring during thermal runaway events. [ABSTRACT FROM AUTHOR]

Separators in lithium‐ion batteries are typically considered to be electrochemically inert under normal operating conditions. Yet, temperature abuse tests at elevated temperatures of ca. 60 °C to 132 °C show that the choice of separator material has a decisive influence on battery behavior and degradation. Using online electrochemical mass spectrometry, we analyzed the evolution of cell voltage and gas products during and after thermal abuse for different separators. Polypropylene and polytetrafluoroethylene seem exhibited little change in gas evolution, producing only modest amounts of CO2 and POF3. In contrast, glass fiber and polyethylene terephthalate separators caused additional gas release, indicating electrochemical instability. Polyethylene terephthalate produced significantly more gas, resulting in the mechanical failure of the separator and drastic performance losses. The amount of CO2 evolved with polyethylene terephthalate is four times higher than that of the glass fiber separator. However, the amount of POF3 detected was five times higher for the glass fiber separator. [ABSTRACT FROM AUTHOR]

Abstract Alleviating the decomposition of the electrolyte is of great significance to improving the cycle stability of cathodes, especially for LiCoO2 (LCO), its volumetric energy density can be effectively promoted by increasing the charge cutoff voltage to 4.6 V, thereby supporting the large‐scale application of clean energy. However, the rapid decomposition of the electrolyte under 4.6 V conditions not only loses the transport carrier for lithium ion, but also produces HF and insulators that destroy the interface of LCO and increase impedance. In this work, the decomposition of electrolyte is effectively suppressed by changing the adsorption force between LCO interface and EC. Density functional theory illustrates the LCO coated with lower electronegativity elements has a weaker adsorption force with the electrolyte, the adsorption energy between LCO@Mg and EC (0.49 eV) is weaker than that of LCO@Ti (0.73 eV). Meanwhile, based on the results of time of flight secondary ion mass spectrometry, conductivity‐atomic force microscopy, in situ differential electrochemical mass spectrometry, soft X‐ray absorption spectroscopy, and nuclear magnetic resonance, as the adsorption force increases, the electrolyte decomposes more seriously. This work provides a new perspective on the interaction between electrolyte and the interface of cathode and further improves the understanding of electrolyte decomposition.

This study explores how fluoroethylene carbonate (FEC) influences the solid electrolyte interface (SEI) layer formation during battery cycling process. FEC improves SEI properties, producing a uniform, chemically stable layer enriched with lithium fluoride. This enhances mechanical resilience and electrochemical stability. FEC also suppresses electrolyte deformation and decomposition, maintaining its initial state. The findings highlight the significance and comprehension of electrolyte additives, offering an electrolyte research pathway for improving Li-ion battery performance and durability.

The increasing need for electrochemical energy storage drives the development of post‐lithium battery systems. Among the most promising new battery types are sodium‐based battery systems. However, like its lithium predecessor, sodium batteries suffer from various issues like parasitic side reactions, which lead to a loss of active sodium inventory, thus reducing the capacity over time. Some problems in sodium batteries arise from an unstable solid electrolyte interphase (SEI) reducing its protective power e. g., due to increased solubility of SEI components in sodium battery systems. While it is known that the electrolyte affects the SEI structure, the exact formation mechanism of the SEI is not yet fully understood. In this study, we follow the initial SEI formation on a piece of sodium metal submerged in propylene carbonate with and without the electrolyte salt sodium perchlorate. We combine X‐ray photoelectron spectroscopy, gas chromatography, and density functional theory to unravel the sudden emergence of propylene oxide after adding sodium perchlorate to the electrolyte solvent. We identify the formation of a sodium chloride layer as a crucial step in forming propylene oxide by enabling precursors formed from propylene carbonate on the sodium metal surface to undergo a ring‐closing reaction. Based on our combined theoretical and experimental approach, we identify changes in the electrolyte decomposition process, propose a reaction mechanism to form propylene oxide and discuss alternatives based on known synthesis routes. [ABSTRACT FROM AUTHOR]

Electrolyte engineering is a fascinating choice to improve the performance of Li‐rich layered oxide cathodes (LRLO) for high‐energy lithium‐ion batteries. However, many existing electrolyte designs and adjustment principles tend to overlook the unique challenges posed by LRLO, particularly the nucleophilic attack. Here, we introduce an electrolyte modification by locally replacing carbonate solvents in traditional electrolytes with a fluoro‐ether. By benefit of the decomposition of fluoro‐ether under nucleophilic O‐related attacks, which delivers an excellent passivation layer with LiF and polymers, possessing rigidity and flexibility on the LRLO surface. More importantly, the fluoro‐ether acts as "sutures", ensuring the integrity and stability of both interfacial and bulk structures, which contributed to suppressing severe polarization and enhancing the cycling capacity retention from 39 % to 78 % after 300 cycles for the 4.8 V‐class LRLO. This key electrolyte strategy with comprehensive analysis, provides new insights into addressing nucleophilic challenge for high‐energy anionic redox related cathode systems. [ABSTRACT FROM AUTHOR]

Non-aqueous electrolyte liquids such as carbonate solvents have been widely employed in the commercial lithium-ion batteries and in the development of next-generation rechargeable batteries. The decomposition products of the organic electrolyte and additive molecules contribute to the formation of solid electrolyte interphases (SEIs) on the electrode surface, which have key impacts on battery's electrochemical performance. The rational engineering of electrolyte systems demands precise understanding of the electrochemical reaction pathways as well as the decomposition products of the electrolytes. Mass spectrometry (MS) is a well-established molecular analytical approach that can provide critical information for unambiguous structure assignment based on its mass-resolving power. In recent years, the application of MS for battery research has been expanding rapidly, providing valuable insights about the chemical species generated during battery operation and electrolyte evolution. This review aims to summarize the recent advances of MS technique-based analysis of electrolyte decomposition products as well as SEIs, and thus to demonstrate the high utility of MS methods for characterization of battery systems.

Lithium nitrate is an attractive lithium additive in the construction of high‐performance lithium metal anodes with a Li3N‐rich solid electrolyte interphase (SEI) layer. However, the eight‐electron transfer process induces high energy barriers between LiNO3 and Li3N. Herein, the inner Helmholtz plane is tuned on a Li deposition host to attain sluggish/rapid LiNO3 decomposition kinetics, resulting in different intermediate content distributions of Li species in the SEI. Notably, lithium oxynitride (LiNO) is identified as the decomposition intermediate, and experimental and simulation results confirm its role in obstructing LiNO3 decomposition. Moreover, the results reveal that the dipole–dipole interaction between LiNO and the polar V≡N bond can change the ionic/covalent character of the N═O bonds, considerably facilitating the energy transfer process of the N═O cleavage, and promoting a LiNO3 reduction to achieve a Li3N‐rich SEI. Consequently, when the electrolyte contains 0.37 m LiNO3, dendrite, and dead Li formation are suppressed effectively with the VN system, and an average Coulombic efficiency of 99.7% over 1000 cycles (1 mA cm−2, 1 mAh cm−2) can be attained. These results can promote the nitride oxidation break process and pave the way for fabricating high‐performance Li3N‐rich lithium metal batteries. [ABSTRACT FROM AUTHOR]

LiNiO2‐based high‐nickel layered oxide cathodes are regarded as promising cathode materials for high‐energy‐density automotive lithium batteries. Most of the attention thus far has been paid towards addressing their surface and structural instability issues brought by the increase of Ni content (>90 %) with an aim to enhance the cycle stability. However, the poor safety performance remains an intractable problem for their commercialization in the market, yet it has not received appropriate attention. In this review, we focus on the gas generation and thermal degradation behaviors of high‐Ni cathodes, which are critical factors in determining their overall safety performance. A comprehensive overview of the mechanisms of outgassing and thermal runaway reactions is presented and analyzed from a chemistry perspective. Finally, we discuss the challenges and the insights into developing robust, safe high‐Ni cathodes. [ABSTRACT FROM AUTHOR]

Highlights The composite cathode composition, preparation method, and chemical compatibility play critical roles in constructing triple-phase interfaces. Understanding the electrolyte degradation is critical for boosting the high-performance composite sulfur cathode. The volume change of sulfur challenges the mechanical stability of composite sulfur cathode.

Highlights: The composite cathode composition, preparation method, and chemical compatibility play critical roles in constructing triple-phase interfaces. Understanding the electrolyte degradation is critical for boosting the high-performance composite sulfur cathode. The volume change of sulfur challenges the mechanical stability of composite sulfur cathode. Lithium–sulfur batteries with liquid electrolytes have been obstructed by severe shuttle effects and intrinsic safety concerns. Introducing inorganic solid-state electrolytes into lithium–sulfur systems is believed as an effective approach to eliminate these issues without sacrificing the high-energy density, which determines sulfide-based all-solid-state lithium–sulfur batteries. However, the lack of design principles for high-performance composite sulfur cathodes limits their further application. The sulfur cathode regulation should take several factors including the intrinsic insulation of sulfur, well-designed conductive networks, integrated sulfur-electrolyte interfaces, and porous structure for volume expansion, and the correlation between these factors into account. Here, we summarize the challenges of regulating composite sulfur cathodes with respect to ionic/electronic diffusions and put forward the corresponding solutions for obtaining stable positive electrodes. In the last section, we also outlook the future research pathways of architecture sulfur cathode to guide the develop high-performance all-solid-state lithium–sulfur batteries. [ABSTRACT FROM AUTHOR]

Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF2 and polymer‐derived carbon (FeF2@PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod‐shaped FeF2 embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF2@PDC enables a reversible capacity of 500 mAh g–1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF2@PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g–1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe3O4 layers on the surface of FeF2 prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF2 electrochemistry, and a strategy to radically improve the electrochemical performance of FeF2 cathode for lithium‐ion battery applications. [ABSTRACT FROM AUTHOR]

Lithium‐rich disordered rocksalts (DRX) are a promising class of cathode materials for high‐energy lithium ion batteries (LIBs) and lithium metal batteries (LMBs) due to the high initial specific capacities (>200 mAh g−1) as well as flexible chemical composition. However, challenges concerning severe capacity fade and voltage decay upon cycling at high cut‐off voltages are still to be overcome. Moreover, state‐of‐the‐art carbonate‐based electrolytes can be decomposed by reactive oxygen species released by DRX materials during cycling. In this work, the electrochemical performance of Li1.25Fe0.5Nb0.25O2 (LFNO) || Li LMB and LFNO || graphite LIB cells is compared for a conventional, carbonate‐based electrolyte and the solvate ionic liquid (SIL) [Li(G3)][TFSI] (G3: triethyleneglycoldimethylether). Cycle life is notably improved by the chemically more stable ionic liquid electrolyte, as the anionic redox activity of LFNO is prolonged compared to the carbonate‐based cells. This work represents an important step toward an improved cycle life of DRX cathodes. [ABSTRACT FROM AUTHOR]

Electrolyte decomposition and electrode corrosion stand as two primary side reactions in lithium‑oxygen (Li O 2) batteries during their discharge/charge cycles. In this work, a comprehensive Li O 2 battery model combining multi-step lithium peroxide (Li 2 O 2) formation, electrolyte decomposition, and electrode corrosion is proposed. Based on this model, the deposition behaviors and cycling performance of the Li O 2 battery under deep discharge/charge cycles are investigated. The stop of discharge is mainly ascribed to the loss of active surface area for the battery using tetraethylene glycol dimethyl ether (TEGDME) electrolyte, while both O 2 transport limitation and active surface area loss lead to the discharge termination for battery using dimethyl sulfoxide (DMSO) electrolyte. The incomplete decomposition of Li 2 O 2 and lithium carbonate (Li 2 CO 3) clogs electrode pores, leading to a continuous decline in the discharge capacity of the Li O 2 battery. For the TEGDME-based battery, the undecomposed Li 2 CO 3 gradually dominates the deposition with cycles, wherein electrode corrosion becomes the primary source of the undecomposed Li 2 CO 3 after 3 cycles. For the DMSO-based battery, undecomposed Li 2 O 2 is always a dominant trigger for battery discharge capacity degradation, although electrode corrosion remains a key contributor to Li 2 CO 3 generation. Despite the DMSO-based battery exhibiting lower rates of electrolyte decomposition and electrode corrosion, it demonstrates poorer cyclic performance than the TEGDME-based battery due to the generation of more toroidal Li 2 O 2. Moreover, when the charging cut-off voltage is reduced to 4.2 V, discharge capacity diminishes more rapidly due to the increased accumulation of undecomposed Li 2 O 2 , despite suppressed Li 2 CO 3 deposition. Finally, the results confirm that thick electrodes lead to deteriorating cycling performance, stemming from increased discharge/charge overpotential and extended discharge/charge times, thus intensifying the side reactions. • A multi-step discharge/charge Li-O 2 battery model involving electrolyte decomposition and electrode corrosion reactions is proposed. • Deposition/decomposition behaviors of Li 2 O 2 and Li 2 CO 3 from different reaction pathways with cycles are explored. • Mechanisms of discharge capacity degradation and discharge/charge failure under different conditions are revealed. [ABSTRACT FROM AUTHOR]

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 LiPF 6 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. [Display omitted] • FEC as a co-solvent significantly reduces electrolyte decomposition. • DMC/FEC blend outperforms traditional formulations in capacity retention. • FEC forms a stable, LiF-rich SEI, improving the chemical stability of LICs. • FEC lowers gas production during electrolyte decomposition. • FEC-based electrolytes boost thermal stability and safety under abusive conditions. [ABSTRACT FROM AUTHOR]

Abstract Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF2 and polymer‐derived carbon (FeF2@PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod‐shaped FeF2 embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF2@PDC enables a reversible capacity of 500 mAh g–1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF2@PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g–1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe3O4 layers on the surface of FeF2 prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF2 electrochemistry, and a strategy to radically improve the electrochemical performance of FeF2 cathode for lithium‐ion battery applications.

Electrolyte decomposition significantly impacts the long-term stability of Li-ion batteries, generating liquid and gaseous byproducts. This study focuses on formaldehyde formation, a critical byproduct from CO 2 reduction in Ni-rich Li-ion batteries. Through experimental and computational analyses, formaldehyde emerges from carbonate-based electrolyte decomposition. Examining overcharge, over-discharge, and fast charging conditions, formaldehyde concentration sharply increases under overcharge, indicating severe electrolyte breakdown, while over-discharge shows a gradual rise. Fast charging similarly elevates formaldehyde levels, underscoring the link between electrolyte decomposition and abusive conditions. Importantly, this research proposes utilizing formaldehyde concentration from the initial cycle as a predictive marker for assessing long-term Ni-rich Li-ion battery stability trends. Elevated initial formaldehyde indicates potential capacity fade and accelerated degradation, enabling proactive mitigation strategies. The study elucidates mechanisms governing formaldehyde formation, providing a foundation for developing electrolyte formulations and electrode materials with enhanced decomposition resistance and improved stability. This investigation contributes to the fundamental understanding of electrolyte decomposition in Ni-rich Li-ion batteries and presents a novel approach to predicting long-term performance based on initial formaldehyde measurements, advancing high-performance and reliable energy storage solutions. [Display omitted] • Formaldehyde predicts stability in Ni-rich Li-ion batteries under stress. • CO 2 reduction to formaldehyde marks electrolyte decomposition's critical pathway. • Overcharge significantly accelerates formaldehyde production, hinting at rapid degradation. • Precise formaldehyde measurement via NMR improves battery health evaluation. • Research inspires advanced battery designs limiting formaldehyde generation. [ABSTRACT FROM AUTHOR]

Ni-rich cathodes are essential for the advancement of high-energy lithium-ion batteries but encounter significant challenges at elevated voltages, including oxygen liberation and enhanced surface reactivity, which precipitate electrolyte decomposition. This study explores the intricate reaction mechanisms of electrolyte decomposition linked to the pronounced release of oxygen from the cathode lattice in large-scale 18650 cylindrical cells employing Ni-rich LiNi 0.90 Mn 0.05 Co 0.05 O 2 (NMC90)//graphite configurations, focusing on electrode crosstalk effects at high voltages. Notably, acetals such as methoxy methanol (49.93 %) and methane diol (50.07 %) were identified at 4.7 V, with their presence escalating at 4.9 V. Formaldehyde, present at 7.21 %, along with methanol (22.77 %), methane diol (36.35 %), and methoxy methanol (33.67 %), begins to manifest at 4.9 V. The dissolution of transition metals was analyzed using Inductively Coupled Plasma Atomic Emission Spectrometry, and changes in the double-layer capacitance were assessed through electrochemical impedance spectroscopy, further validating the link between these decomposition products and cathode failure associated with oxygen release. These insights reveal the complex relationship between electrolyte decomposition and cathode degradation due to oxygen release, highlighting a critical failure mechanism in large-scale cylindrical lithium-ion batteries. [Display omitted] • Formaldehyde, acetals indicate high-voltage cathode degradation. • Cathode oxygen release correlates with electrolyte decomposition, impacts battery. • Spectroscopic analysis connects transition metal dissolution, cathode failure. • Capacitance variation used for precise battery diagnostics, indicates degradation. • Increased metal dissolution linked to microcracking, expands surface area. [ABSTRACT FROM AUTHOR]

[Display omitted] • FEC builds SEI layer with Li 2 CO 3 and LiF on electrode, whether graphite or silicon. • The durable SEI layer enhances capacity and effectively reduces volume expansion. • FEC prevents the chemical conversion and reductive decomposition of electrolyte. • FEC inhibits dicarboxylate formation, thereby preserving electrolyte performance. This study explores how fluoroethylene carbonate (FEC) influences the solid electrolyte interface (SEI) layer formation during battery cycling process. FEC improves SEI properties, producing a uniform, chemically stable layer enriched with lithium fluoride. This enhances mechanical resilience and electrochemical stability. FEC also suppresses electrolyte deformation and decomposition, maintaining its initial state. The findings highlight the significance and comprehension of electrolyte additives, offering an electrolyte research pathway for improving Li-ion battery performance and durability. [ABSTRACT FROM AUTHOR]

• Ca-based hybrid interface (CHI) of about 5 nm is constructed by a facile adsorption and topochemical conversion process. • Commercial LiFePO 4 with CHI exhibited superior stability and retention of coulombic efficiency of about 99.9%. • The CHI evolved into a stable Ca-based cathode electrolyte interphase, which inhibited uncontrolled electrolyte decomposition. • High initial coulombic efficiency, stable cycling performance, and good rate performance were also simultaneously achieved. In rechargeable batteries, there are many electrodes exhibiting good ion-storage performance under mild conditions. However, uncontrolled electrolyte decomposition (UED) will hardly be avoided once harsh conditions, e.g., high-voltage, thick electrode, large rate, long cycle, etc., are adopted to pursue possible breakthrough in energy and power. Here, take commercial LiFePO 4 (pristine LiFePO 4) as an example, UED due to progressive cracking which resulted from long-term and repetitive structure deformation, large rate, thick electrode, and overcharge, was prevented by uniform encapsulation of Ca-based hybrid interfaces (CHI). Li-metal batteries with Ca-modified LiFePO 4 cathodes delivered much higher (initial coulombic efficiency of 98.0 % vs. 94.5 % at 20 mA g−1), and more stable coulombic efficiencies (99.11 %-100.03 % vs. 96.05–98.79 % at 50 mA g−1 for 100 cycles) than those of pristine ones at wide window voltage of 2.0–4.2 V. Li-ion batteries with Ca-modified LiFePO 4 cathodes and graphite anodes even presented stable coulombic efficiencies of 99.9 % for more than 400 cycles at high areal capacity (2.66 mAh cm−2), thick electrode (active material ≈18 mg cm−2), and large rates (0.18–3.6 mA cm−2). The ultrastable Ca-based cathode electrolyte interphases (Ca-CEIs) evolved from CHIs accounts for the good retention of coulombic efficiencies. [ABSTRACT FROM AUTHOR]

Analysis of the performance evolution and failure mechanisms of commercial Li-ion batteries is crucial for improving testing methods, accurately modeling battery performance, and ensuring safe battery operation. Here, we present the results of a 2-year aging study conducted on commercial large-format LiNiMnCoO 2 -graphite pouch cells. Loss of lithium inventory (LLI) and loss of positive electrode active material (LAM PE) are shown to dominate capacity fade, as quantified by differential voltage-capacity analysis; only a small amount of LAM PE was measured in extracted electrode material, indicating that LAM PE in full cells was due to electrode dry-out. Resistance evolution, observed by direct current pulses and electrochemical impedance spectroscopy analyzed using the distribution of relaxation times, shows complex trends. Particle cracking and electrode expansion is theorized to cause most changes to resistance. Post-mortem measurements reveal a 10% increase in electrode stack thickness and substantial gas generation, with lithium plating observed in extreme cycling conditions, causing large resistance increases. Circumstantial evidence for self-discharge via redox shuttle, which decomposes the electrolyte, is shown. Overall, electrolyte stability was determined to be the limiting factor for cell lifetime. The impacts of many degradation mechanisms on diagnostic signals substantially overlap, making it challenging to monitor cell health and safety. [Display omitted] • 2-year calendar and cycle aging of commercial large-format lithium-ion pouch cells. • Measurement and analysis of voltage-capacity curves, d.c. pulse, and a.c. impedance. • Aged cells show microstructural damage, thickness increase, and gas generation. • Performance loss driven by SEI growth, failure driven by electrolyte decomposition. • Observed failures include burst pouches and lithium plating induced short-circuit. [ABSTRACT FROM AUTHOR]

Most commercially available lithium ion battery systems and some of their possible successors, such as lithium (metal)-sulfur batteries, rely on liquid organic electrolytes. Since the electrolyte is in contact with both the negative and the positive electrode, its electrochemical stability window is of high interest. Monitoring the electrolyte decomposition occurring at these electrodes is key to understand the influence of chemical and electrochemical reactions on cell performance and to evaluate aging mechanisms. In the context of lithium-sulfur batteries, information about the analysis of soluble species in the electrolytes—besides the well-known lithium polysulfides—is scarcely available. Here, the irreversible decomposition reactions of typically ether-based electrolytes will be addressed. Gas chromatography in combination with mass spectrometric detection is able to deliver information about volatile organic compounds. Furthermore, it is already used to investigate similar samples, such as electrolytes from other battery types, including lithium ion batteries. The method transfer from these reports and from model experiments with non-target analyses are promising tools to generate knowledge about the system and to build up suitable strategies for lithium-sulfur cell analyses. In the presented work, the aim is to identify aging products emerging in electrolytes regained from cells with sulfur-based cathodes. Higher-molecular polymerization products of ether-based electrolytes used in lithium-sulfur batteries are identified. Furthermore, the reactivity of the lithium polysulfides with carbonate-based solvents is investigated in a worst-case scenario and carbonate sulfur cross-compounds identified for target analyses. None of the target molecules are found in carbonate-based electrolytes regained from operative lithium-titanium sulfide cells, thus hinting at a new aging mechanism in these systems. [ABSTRACT FROM AUTHOR]

Alleviating the decomposition of the electrolyte is of great significance to improving the cycle stability of cathodes, especially for LiCoO 2 (LCO), its volumetric energy density can be effectively promoted by increasing the charge cutoff voltage to 4.6 V, thereby supporting the large-scale application of clean energy. However, the rapid decomposition of the electrolyte under 4.6 V conditions not only loses the transport carrier for lithium ion, but also produces HF and insulators that destroy the interface of LCO and increase impedance. In this work, the decomposition of electrolyte is effectively suppressed by changing the adsorption force between LCO interface and EC. Density functional theory illustrates the LCO coated with lower electronegativity elements has a weaker adsorption force with the electrolyte, the adsorption energy between LCO@Mg and EC (0.49 eV) is weaker than that of LCO@Ti (0.73 eV). Meanwhile, based on the results of time of flight secondary ion mass spectrometry, conductivity-atomic force microscopy, in situ differential electrochemical mass spectrometry, soft X-ray absorption spectroscopy, and nuclear magnetic resonance, as the adsorption force increases, the electrolyte decomposes more seriously. This work provides a new perspective on the interaction between electrolyte and the interface of cathode and further improves the understanding of electrolyte decomposition., (© 2024 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

Copyright of Issues of Chemistry & Chemical Technology / Voprosy Khimii & Khimicheskoi Tekhnologii is the property of Ukrainian State University of Chemical Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• In-situ techniques identify soluble products limit LiBOB utilization efficiency. • Mechanism revelation that AC pulse promotes LiBOB complete decomposition. • AC pulse generates a reinforced SEI rich in inorganics and cross-linking polymers. • Synchronized achieving "amount reduction and efficiency increase" of additives. Lithium bis(oxalate)borate (LiBOB) is well known for its protection of graphite anodes in lithium-ion batteries (LIBs) by forming a passivated solid electrolyte interface (SEI) layer. However, the underlying film-formation mechanism of LiBOB remains poorly understood, thereby its utilization efficiency has received little attention. In this work, we resort to in situ techniques to determine the crux of limiting the complete decomposition of LiBOB during the initial SEI formation lies in the BOB-derived soluble products which accumulate on the graphite surface and hinder its subsequent sustained decomposition. Then alternating current pulse (AC) discharge technology is employed to promote the self-decomposition of LiBOB. The complementation results of electrochemical/physical characterizations and theoretical calculations reveal that AC not only facilitates the diffusion of soluble products, but also promotes the synergy reaction of the soluble products with LiPF 6 , generating a smooth and uniform SEI rich in inorganics (LiF and Li x PO y F z) and B-containing cross-linking polymers. More significantly, a thinner SEI is obtained in AC by reducing the LiBOB amount in half. The as-resulted cell exhibits higher rate performance (280 mAh g−1 at 2 C) and better cycling stability (320 mAh g−1 after 200 cycles at 1 C, 98 % capacity retention), synchronously achieving "amount reduction and efficiency increase" of expensive additives. This study provides an entirely novel method for reinforcing the SEI films using external electric fields, and enriches the strategies for improving the performance of LIBs via interfacial engineering. [ABSTRACT FROM AUTHOR]

Most commercially available lithium ion battery systems and some of their possible successors, such as lithium (metal)-sulfur batteries, rely on liquid organic electrolytes. Since the electrolyte is in contact with both the negative and the positive electrode, its electrochemical stability window is of high interest. Monitoring the electrolyte decomposition occurring at these electrodes is key to understand the influence of chemical and electrochemical reactions on cell performance and to evaluate aging mechanisms. In the context of lithium-sulfur batteries, information about the analysis of soluble species in the electrolytes—besides the well-known lithium polysulfides—is scarcely available. Here, the irreversible decomposition reactions of typically ether-based electrolytes will be addressed. Gas chromatography in combination with mass spectrometric detection is able to deliver information about volatile organic compounds. Furthermore, it is already used to investigate similar samples, such as electrolytes from other battery types, including lithium ion batteries. The method transfer from these reports and from model experiments with non-target analyses are promising tools to generate knowledge about the system and to build up suitable strategies for lithium-sulfur cell analyses. In the presented work, the aim is to identify aging products emerging in electrolytes regained from cells with sulfur-based cathodes. Higher-molecular polymerization products of ether-based electrolytes used in lithium-sulfur batteries are identified. Furthermore, the reactivity of the lithium polysulfides with carbonate-based solvents is investigated in a worst-case scenario and carbonate sulfur cross-compounds identified for target analyses. None of the target molecules are found in carbonate-based electrolytes regained from operative lithium-titanium sulfide cells, thus hinting at a new aging mechanism in these systems.

Li metal has been considered a promising anode for high‐energy density batteries because of its high specific capacity. However, uncontrolled Li dendrite growth and severe electrolyte decomposition are detrimental obstacles hindering the practical applications of lithium metal batteries. Herein, electrochemically active red P‐based protective layers are introduced to suppress Li dendrite growth during cycling. Red P particles confined in the protective layer react with Li dendrites, forming Li3P, as Li dendrites are penetrating through the protective layer. As a result, Li metal is no longer plated on the Li3P surface because Li3P is electrically insulating, eventually leading to suppressing Li dendrite growth. Moreover, the red P‐based protective layer is functionalized with dielectric BaTiO3 nanoparticles to scavenge radicals generated from electrolyte decomposition as well as to improve the mechanical strength of protective layers. The synergy effect of electrochemically active red P and inactive BaTiO3 gives rise to the improved short‐circuit time of Li metal and the excellent cycle performance and Coulombic efficiency of Li/Li symmetric and Li/LiFePO4 full cells over 200 cycles, despite the fact that the cell performances are examined with the conventional electrolyte of LiPF6 in ethylene carbonate/diethyl carbonate that is highly unstable against Li metal. [ABSTRACT FROM AUTHOR]

Lithium metal with its high theoretical capacity and low negative potential is considered one of the most important candidates to raise the energy density of all-solid-state batteries. However, lithium filament growth and its induced solid electrolyte decomposition pose severe challenges to realize a long cycle life. Here, dendrite growth in solid-state Li metal batteries is alleviated by introducing a high dielectric material, barium titanate, as a filler that removes the electric field gradients that catalyze dendrite formation. In symmetrical Li-metal cells, this results in a very small over-potential of only 48 mV at a relatively high current density of 1 mA cm−2, when cycling a capacity of 2 mA h cm−2 during 1700 h. The high dielectric filler improves the Coulombic efficiency and cycle life of full cells and suppresses electrolyte decomposition as indicated by solid-state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) measurements. This indicates that the high dielectric filler can suppress dendrite formation, thereby reducing solid electrolyte decomposition reactions, resulting in the observed low overpotentials and improved cycling efficiency. • Dendrite growth in solid Li metal cell is alleviated with a dielectric material. • BaTiO 3 removes the electric field gradients that catalyze dendrite formation. • Small over-potential of 48 mV was obtained at 1 mA/cm2 in symmetric cell. • Solid-state NMR and XPS measurements show eliminated electrolyte decomposition. • Reducing solid electrolyte decomposition results in improved cycling efficiency. [ABSTRACT FROM AUTHOR]

Abstract Three-electrode configurations allow targeted studies of reaction mechanisms, including charge storage in and interphase formation on electrode materials for emerging sodium-ion batteries. However, using sodium metal as a reference electrode results in spontaneous formation of electroactive soluble decomposition products in an ester-based electrolyte. These electrolyte decomposition products undergo oxidation at carbon electrodes at potentials that can be mistaken for reversible sodium (de)intercalation, thus obscuring true measurements of material properties. Graphical abstract Unlabelled Image Highlights • Electrolyte decomposes at Na counter and reference electrodes at open circuit. • Soluble decomposition products oxidized <1 V vs Na/Na+. • Oxidation mimics desirable intercalation currents, creates experimental artifacts. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In operando EPR spectroscopy is utilized to monitor redox processes in LCO. • In the pristine battery, Co2+ due to electrolyte decomposition was found. • A pure oxygen redox mechanism is found for standard battery cycling. • Cobalt remains redox inactive during charging and discharging. Abstract Electron paramagnetic resonance (EPR) spectroscopy was utilized in operando to analyze redox mechanisms in lithium cobalt oxide (LCO) cathode material during battery cycling. In the pristine battery, a considerable amount of paramagnetic Co2+ was detected that was formed during initial contact of the electrolyte with the LCO. The Co2+ got oxidized during the formation cycle. The absence of an EPR signal during subsequent battery cycles, irrespective of the state-of-charge, indicates that no EPR active Co4+ is formed. This suggests the presence of an anionic oxygen redox mechanism in the active material. [ABSTRACT FROM AUTHOR]

The anion storage electrochemistry of carbon cathode is bottlenecked by the severe electrolyte decomposition and significant volume expansion. A surface coating that can impart simultaneous protection against all the drawbacks is challenging to achieve. Herein, the multifaceted benefits of pitch-derived soft carbon are leveraged as a coating layer. An upscalable annealing treatment results in an ultrathin, polycrystalline, uniformly distributed, and porous layer of carbonized pitch on the redox-active core. The coated material demonstrates 25 and 5.5% improvement in capacity retention, and coulombic efficiency, respectively, and a 150 mV reduction in voltage hysteresis. The smooth surface topography of the coated sample alleviates the electrolyte decomposition during high-voltage cycling. The mechanical flexibility of the coated material to withstand the volume change and to preserve the structural integrity are uncovered by the nanoindentation experiments and further supported by the post-cycling characterizations. The coating offers mechanochemical robustness to the interface and minimizes the growth of resistance. The strategy of soft carbon coating on anion-storing cathode can be extended to dual graphite full cells and other anion-storing chemistries irrespective of the anode and electrolyte. [Display omitted] • Pitch derived soft carbon coating is easy to synthesize and upscalable. • The coating layer is 35 nm thin, polycrystalline, and uniformly distributed. • It improves electrochemical performances superiorly. • It enhances interfacial stability and withstands volume change. • The concept can be extrapolated to all anion storing battery chemistries. [ABSTRACT FROM AUTHOR]

Impacts of environmental relative humidity (RH) on lithium nickel-cobalt-aluminum oxide (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) based cell performance is investigated. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathode electrodes are prepared in different environmental relative humidity (RH), 20% RH, 40% RH and 60% RH, respectively. Significant impact of the environmental RH on the cell discharge and coulombic efficiency is observed, specifically, 179.1, 175, and 159.5 mAh/g with the relative humidity, 20% RH, 40% RH and 60% RH, respectively; and corresponding first Coulombic efficiency is 84.9%, 82.2%, and 80.1%. However, the cycling stability of LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode is similar regardless of the environmental RH content. To understand the root cause for the disparity on initial discharge capacity and first Coulombic efficiency, local surface morphology/chemistry of the NCA cathode prepared at different environmental RH has been characterized via multiple advanced techniques, including: SEM, XRD, and XPS. Severe electrolyte decomposition and microstructure changes are seen in the cathode prepared at high moisture content after the first cycle. The severe electrolyte decomposition on the cathode surface and structural degradation of the cathode particles is attributed to the high humidity content. This is believed to be the source of the poor electrochemical performance of NCA cathode. Therefore, environmentally RH control is a critical factor to yield superior electrochemical performance for NCA during electrode processing. [ABSTRACT FROM AUTHOR]

Glyme-based electrolytes with various lithium bis(trifluoromethane) sulfonamide (LiTFSI) salt concentrations have been investigated for their use in Li‑oxygen battery applications. Charge/discharge cycling with a cycle capacity of 500 mAh·g −1 showed an improvement as high as 300% for electrolytes containing higher LiTFSI concentrations. Electrochemical impedance spectroscopy (EIS) studies of Li-O 2 full cells and Raman spectroscopy studies on the discharged cathodes revealed that the superior cyclability at higher LiTFSI contents was due to a decrease in the rate of growth of glyme degradation products (lithium carbonate species). Raman spectroscopy analyses of the electrolytes also suggested that the increase in LiTFSI concentration afforded the formation of cationic and anionic complexes that helped mitigate the tetraglyme degradation. [ABSTRACT FROM AUTHOR]

Abstract: The main limitation of aqueous supercapacitors (SCs) lies in their narrow operating voltages, especially when compared with organic SCs. Fundamental understanding of factors relevant to the operating voltage helps providing guidance for the assembly of high‐voltage aqueous SCs. In this regard, this concept analyzes the deciding factors for the operating voltage of aqueous SCs. Strategies applied to expand the operating voltage are summarized and discussed from the aspects of electrolyte, electrode, and asymmetric structure. Dynamic factors associated with water electrolysis and maximally using the available potential ranges of electrodes are particularly emphasized. Finally, other promising approaches that have not been explored and their challenges are also elaborated, hoping to provide more insights for the design of high‐voltage aqueous SCs. [ABSTRACT FROM AUTHOR]

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr14BF4) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr14TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et4NBF4/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation. [ABSTRACT FROM AUTHOR]

• Capacity fade due to electrolyte degradation and activated carbon transformation. • Passivating degradation products on electrode surface identified. • Surface area and pore property of electrode deteriorated by degradation products. • Defects increased in activated carbon electrode during cycling. The capacity fade mechanism of activated carbon (AC) electrode in Li-ion electrolyte was studied via electrochemical impedance spectroscopy (EIS) and post-mortem electrode characterizations at different stages of electrochemical cycling. Electrochemical cycling was conducted in half cells incorporating the AC working electrode, Li metal counter electrode, and 1 M LiPF 6 in EC:DMC (1:1) electrolyte. Three phases were identified during the ageing process that corresponded with transformation of the passivation layer at the electrode surface and charge transfer impedance derived from the EIS analysis. Surface area and morphology analysis showed that the AC surface was progressively transformed by degradation products that reduced the available surface area and accessibility of electrolyte moieties into the pores. X-ray photoelectron spectroscopy suggested that the degradation products are from the LiPF 6 salt decomposition and carbonate solvent decomposition, while Raman analysis demonstrated increased defects in the electrode as cycling progressed. The capacity fade was therefore caused by the synergistic effect of electrolyte degradation and active material transformation. [Display omitted] [ABSTRACT FROM AUTHOR]

Using flame retardants (FRs) in lithium ion battery (LIB) electrolytes is usually a tradeoff between electrochemical performance and electrolyte flammability. Fluorinated FRs are a promising class of FRs which are currently under investigation. During this work, three FRs originating from triethyl phosphate with varying degree of fluorination were investigated regarding their electrochemical stability on cathode (LiNi 0.33 Co 0.33 Mn 0.33 O 2 , NCM) and anode (graphite) in half cells. During long-term cycling, changes in performance were observed. Especially on the anode side the FR addition showed a decrease in performance in comparison to the standard electrolyte (DEC/EC 1:1, 1M LiPF 6 ). The electrolytes containing the three FRs were extracted from the cells and analyzed regarding their changes in composition and structural degradation. The decomposition products were investigated by gas chromatography (GC) with electron impact (EI) ionization and mass selective (MS) detection. To obtain more information with regard to the identification of unknown decomposition products further GC‐MS experiments with positive chemical ionization (PCI) and negative chemical ionization (NCI) were performed. Twelve different volatile organic decomposition products were identified. These decomposition products can be subdivided regarding their basic structure. Ether based, carbonate based and phosphate based fluorinated and non-fluorinated decomposition products were identified. Furthermore, possible formation pathways for all groups of decomposition products were postulated taking existing literature into account. [ABSTRACT FROM AUTHOR]

Experimental data elucidating the time-dependent composition of the electrolyte within a standard lithium-sulfur battery cell are presented. The electrolyte employed consisted of a solution of LiTFSI in a 1:1 mixture of dimethoxyethane and dioxolane, including nitrate salts. In order to track the decomposition reactions of the electrolyte components, the cells were run for a fixed number of cycles, after which they were opened and the remaining electrolyte was extracted with an excess amount of 1,4-dioxane. The amount of each of the components (namely LiTFSI, dimethoxyethane and dioxolane) within these mixtures was determined by means of gas chromatography and 19 F-NMR. It was found that the amount of electrolyte accessible to extraction remains relatively constant during the first 25 cycles, but then continuously decreases within the subsequent 40 investigated cycles. The ratio of the organic constituents of the electrolyte does not change considerably, which means there is no preferred decomposition pathway for either of the two components dioxolane and dimethoxyethane, respectively. These results demonstrate that the capacity fading of a lithium-sulfur cell coincides with the loss of the electrolyte within the cell and there is a strong correlation between the failure of a lithium-sulfur cell and the decomposition reactions of its electrolyte. These findings are supported by a detailed analysis of the gaseous decomposition products after specified cycle numbers. Realistic pouch bag cells are used as test vehicles. Such cells do resemble industrially viable, commercial cells much closer as e.g. coin-type cells: Much lower electrolyte/active mass ratios can be used, thus allowing for a more realistic picture of the failure mechanisms involved. [ABSTRACT FROM AUTHOR]

The aging products of the electrolyte from a commercially available state-of-the-art 18650-type cell were investigated. During long term cycling a huge difference in their performance and lifetime at different temperatures was observed. By interpretation of a strong capacity fading of cells cycled at 20 °C compared to cells cycled at 45 °C a temperature depending aging mechanism was determined. To investigate the influence of the electrolyte on this fading, the electrolyte was extracted by supercritical fluid extraction (SFE) and then analyzed by gas chromatography (GC) with electron impact (EI) ionization and mass selective detection. To obtain more information with regard to the identification of unknown decomposition products further analysis with positive chemical ionization (PCI) and negative chemical ionization (NCI) was performed. 17 different volatile organic aging products were detected and identified. So far, seven of them were not yet known in literature and several formation pathways were postulated taking previously published literature into account. [ABSTRACT FROM AUTHOR]

In this work, the commercial LiFePO 4 /graphite batteries are cycled under C/3 rate at room temperature (25 °C), 35 °C, 45 °C and 55 °C respectively, and the cycle lifetime is 615 days, 404 days, 159 days and 86 days respectively, which indicates that the capacity fade is strongly dependent upon the ambient temperature. The degradation mechanism of battery capacity is analyzed by the electrochemical and physical characterization. At room temperature, the major reason for the capacity fade of full cells is the irreversible loss of active lithium due to the generation and reformation of SEI film. However, when the ambient temperature exceeds 35 °C, the electrolyte decomposition is greatly enhanced by the elevated temperature which could significantly accelerate and dominate the consumption rate of active lithium. Meanwhile, the elevated temperature has an adverse influence on the performance of LiFePO 4 material. In addition, the proportions of effects caused by structure degradation and the surface layer for single electrodes are calculated respectively. Through a series of testing experiments, it is concluded that the degradation mechanism is changed when the test temperature is equal or higher than 45 °C, and the elevated temperature is not a suitable stress factor to accelerate the aging of full cells. [ABSTRACT FROM AUTHOR]

• The continuously growing CEI layer exhibits gradually increasing LiF as the main composition in DRX cathode materials. • The significant change of the CEI layer is closely related to loss of lattice oxygen (O2−), the continuous over-reduction of redox-active TMs from the cathode surface, severe TMs dissolution, and the release of CO 2 /O 2 , and irreversible phase transition in surface structures. Li-rich cation-disordered rock-salt oxides (DRXs) are promising candidates for next-generation Li-ion cathode materials due to the demonstrated high capacity (> 300 mAh g−1) by utilizing both transition metal (TM) cations and oxygen anions with a much-widened material design space as compared to conventional layered cathodes, which heavily rely on Co and Ni. However, the serious performance deterioration during long-term cycling impedes their practical applications. Although oxygen loss and associated densified surface layer are responsible for the performance deterioration, these issues are part of the scope of cathode electrolyte interface (CEI) which need further study, including its chemical composition, chemical and electrochemical stability, formation mechanism as well as the effects on battery performance. Through careful monitoring of the CEI evolution of Li 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO) in conventional carbonated-based electrolyte upon charging and discharging, we identify that the continuously growing CEI layer exhibits gradually increasing LiF as the main composition. The significant change of the CEI layer is closely related to loss of lattice oxygen (O2−), the continuous over-reduction of redox-active TMs (e.g. Mn3+, Mn 4+) from the cathode surface, severe TMs dissolution, and the release of CO 2 /O 2 , and irreversible phase transition in surface structures, which eventually cause a fast capacity degradation and voltage decay. This research provides a fundamental interpretation for understanding interfacial stability in this young class of DRX cathode materials. [ABSTRACT FROM AUTHOR]