Ethylene Carbonate-dimethyl Carbonate Research Articles

Rational Design of Electrolyte Additives for Improved Solid Electrolyte Interphase Formation on Graphite Anodes: A Study of 1,3,6-Hexanetrinitrile

The construction of a thin, uniform, and robust solid electrolyte interphase (SEI) film on the surface of active materials is pivotal for enhancing the overall performance of lithium-ion batteries (LiBs). However, conventional electrolytes often fail to achieve the desired SEI characteristics. In this work, we introduced 1,3,6-hexanetrinitrile (HTCN) in the baseline electrolyte (BE) of 1.0 M LiPF6 in Ethylene Carbonate/Dimethyl Carbonate (EC/DMC) (3:7 by volume) with 5 wt.% fluoroethylene carbonate (FEC), denoted as BE-FH. By systematically investigating the influence of FEC: HTCN weight ratios on the electrochemical performance of graphite anodes, we identified an optimal composition (FEC:HTCN = 5:4 by weight, denoted as BE-FH54) that demonstrated greatly improved initial Coulombic efficiency, rate capability, and cycling stability compared with the baseline electrolyte. Deviations from the optimal FEC:HTCN ratio resulted in the formation of either small cracks or excessively thick SEI layers. The enhanced performance of BE-FH54-based LiB is mainly ascribed to the synergistic effect of FEC and HTCN in forming a robust, thin, homogeneous, and ion-conducting SEI. This research highlights the importance of rational electrolyte design in enhancing the electrochemical performance of graphite anodes in LiBs and provides insights into the role of nitrile-based additives in modulating the SEI properties.

Interfacial modulation of bifunctional electrolyte additive engineering for dendrite-free and robust lithium metal anode

Anode materials for rechargeable electric car batteries are obtained from Li-metal owing to their extremely high specific capacity and low redox potential. Unfortunately, safety concerns related to dendrite formation on the anode surface caused by the uneven distribution of Li-ions during the discharge process interfere with the use of Li-metal in industrial batteries. In this study, methyl vinyl sulfone (MVS), a sulfone-based functional electrolyte additive, is used in an additive engineering strategy to control Li-electrolyte interactions and address the aforementioned problems. Li dendrite growth may be restricted, and transition metal degradation on the surface of the cathode can be reduced by the MVS-derived functional electrolyte additive interfacial layer. The electrochemical performance of an ethylene carbonate/dimethyl carbonate (EC/DMC) + 1 wt% MVS Li-metal anode of a Li||Li symmetric cell exhibits remarkable cycle stability, maintaining a low overvoltage for over 750 h at 1 mA cm−2, and capacity of 1 mA h cm−2. Additionally, LiNi0.8Co0.1Mn0.1O2 (NCM811) full cells with the MVS additive exhibit enhanced electrochemical stability for 250 cycles at a current density of 100 mA g−1. This study provides an innovative approach for stabilizing the metal-electrolyte interfacial layer that may be used for practical applications in metal-based rechargeable batteries.

UV-cured gel polymer electrolytes based on poly (ethylene glycol) and organo-modified nanoclays for lithium ions batteries

Next-generation electrolytes for Lithium Ion Batteries (LIBs) must provide increased durability, reliability, safety, and scalability to meet the even more stringent technical requirements of crucial industries such as e-mobility. A promising strategy to merge these technical needs is the development of easy-to-prepare gel polymer electrolytes (GPEs) able to ensure satisfactory conductivity, high stability, and reduced flammability. In this study, we propose the preparation of novel nanocomposite GPEs through one-pot in-situ photo-polymerization (UV-curing), which turns out to be of great interest due to its low-cost, solvent-free and energy-saving characteristics. Poly (ethylene glycol) dimethacrylate (PEG-DMA) was used as hosting polymer matrix, while 1 M Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in ethylene carbonate/dimethyl carbonate (EC/DMC) was used as electrolyte solution. Organo-modified montmorillonite (fMt, intercalated with CTAB) was synthesized and tested as a nanofiller. Both materials and GPEs were characterized by a combination of experimental techniques including FTIR, XRD, SEM, and DMA. Noteworthy, a thorough and systematic study of the lithium-ion transport properties in the prepared GPEs was carried out using pulsed-field gradient nuclear magnetic resonance (PFG-NMR) and electrochemical impedance spectroscopy (EIS). This preliminary study demonstrated the gP-fMt combines ease of preparation and excellent safety (i.e., thermomechanical stability up to 250 °C and nonflammability) with satisfactory lithium transport properties.

A novel calculation strategy for optimized prediction of the reduction of electrochemical window at anode

The reduction of the electrochemical window (EW) of electrolytes plays a significant role in assessing their compatibility with the anode in lithium-ion batteries. However, the accurate calculation of the reduction of EW is still challenging due to missing the solvation effects, condensation effects, kinetic factors, and the passivation on anodes. The theoretical prediction of the intrinsic and apparent EW is confirmed by a comprehensive experimental analysis of ethylene carbonate-dimethyl carbonate (EC-DMC) electrolytes, combining linear sweep voltammetry (LSV) and gas chromatography-mass spectrometry (GC-MS). The proposed novel kinetic normal distribution theory model can quantitatively explain the current density from LSV and affirm acetaldehyde (MeCHO) as one of the primary reduction products of EC. The solvent effect restricts the intrinsic EW of EC-DMC without lithium salt to 2.6 V (vs. Li+/Li) arising from the Marcus–Gerischer theory and the passivation of MeCHO on the anode broadens the apparent EW to 0.3 V (vs. Li+/Li) arising from the normal distribution of the lowest unoccupied molecular orbital (LUMO) for MeCHO produced by thermal motion. In addition, the passivation on the anode depends intensively on the lithium salt, resulting in more complicated influences on the apparent EW.

Synergy Effect of High-Stability of VS4 Nanorods for Sodium Ion Battery.

Sodium-ion batteries (SIBs) have attracted increasing interest as promising candidates for large-scale energy storage due to their low cost, natural abundance and similar chemical intercalation mechanism with lithium-ion batteries. However, achieving superior rate capability and long-life for SIBs remains a major challenge owing to the limitation of favorable anode materials selection. Herein, an elegant one-step solvothermal method was used to synthesize VS4 nanorods and VS4 nanorods/reduced graphene oxide (RGO) nanocomposites. The effects of ethylene carbonate/diethyl carbonate(EC/DEC), ethylene carbonate/dimethyl carbonate(EC/DMC), and tetraethylene glycol dimethyl ether (TEGDME) electrolytes on the electrochemical properties of VS4 nanorods were investigated. The VS4 nanorods electrodes exhibit high specific capacity in EC/DMC electrolytes. A theoretical calculation confirms the advance of EC/DMC electrolytes for VS4 nanorods. Significantly, the discharge capacity of VS4/RGO nanocomposites remains 100 mAh/g after 2000 cycles at a large current density of 2 A/g, indicating their excellent cycling stability. The nanocomposites can improve the electronic conductivity and reduce the Na+ diffusion energy barrier, thereby effectively improving the sodium storage performance of the hybrid material. This work offers great potential for exploring promising anode materials for electrochemical applications.

Optimizing the Electrolyte Systems for Na3 (VO1-x PO4 )2 F1+2x (0≤x≤1) Cathode and Understanding their Interfacial Chemistries Towards High-Rate Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have been regarded as promising alternative to lithium-ion batteries (LIBs) due to the abundance of sodium resource and cost-effectiveness of electrode manufacture. Na3 (VO1-x PO4 )2 F1+2x (0≤x≤1, NVPF1+2x ) polyanionic material, a potential high-energy-density cathode, has shown superior electrochemical performances for advanced SIBs due to its high working voltage (>3.9 V). Electrolyte composition, which plays an indispensable and critical role in determining the cycle stability and the electrode/electrolyte interfacial properties, is of great significance to possess good compatibility with electrode materials, especially the NVPF1+2x cathode. Here, different electrolyte systems, including commonly used 1.0 m NaPF6 /diglyme (NP-005), 1.0 m NaPF6 /propylene carbonate (PC)/5.0 % fluoroethylene carbonate (FEC) (NP-009), 1.0 m NaClO4 /ethylene carbonate-dimethyl carbonate (EC-DMC; 1 : 1 v/v)/5.0 % FEC (NC-019), and 1.0 m NaClO4 /PC (NC-013), were systematically investigated and compared for NVPF1+2x cathode. NVPF1+2x electrode with NP-009 electrolyte showed a superior cycle stability and rate capability at 1-10 C (1 C=130 mA g-1 ) than that of NC-019 and NC-013, while NVPF1+2x electrode with NP-005 electrolyte showed the best high-rate capability at 20-50 C. The cathode/electrolyte interphase (CEI), post-mortem electrode morphology, and electrochemical kinetic characteristics of NVPF1+2x electrode with different electrolytes were profoundly investigated and compared. It demonstrated that NVPF1+2x electrode with NP-005 exhibited a thin, efficient, and NaF-rich CEI layer with less polarization, smaller interfacial resistance, and faster Na+ diffusion than that of NC-019 and NC-013 since they suffered from a thick, overgrown CEI layer due to the consecutive decomposition of FEC, NaClO4 , and/or linear DMC, resulting in inferior electrochemical performance. This work provides new insights for the battery community to gain more comprehensive understanding about the compatibility and interfacial chemistry between different electrolyte systems and various electrode surfaces.

Thermal Degradation Kinetics Analysis of Polymer Composite Electrolyte Membranes of PEVOH and PBT Nano Fiber.

The thermal degradation kinetics of high-performance polymer composite electrolyte membranes were investigated by thermal gravimetric analysis in this study. The novel porous polymer composite membranes were fabricated by crosslinking poly (ethylene-co-vinyl alcohol) (EVOH) with polybutylene terephthalate (PBT) nano fiber. The PBT nano-scale fiber non-woven cloth was first prepared by the electrospinning method to form a labyrinth-like structure, and the crosslinking was carried out by filtering it through a solution of EVOH and crosslinking agent triallylamine using the Porcelain Buchner funnel vacuum filtration method. The PBT–EVOH composite membranes with various crosslinking agent ratios and ethylene carbonate/dimethyl carbonate (EC/DMC) immersion times were investigated for their thermal stability and ionic conductivity. The results showed that the higher crosslinking agent content would lower the crystallinity and enhance thermal stability. The thermal degradation activation energy was dramatically increased from 125 kJ/mol to 340 kJ/mol for the 1.5% crosslinking agent content sample at 80% conversion. The triallylamine crosslinking agent was indeed effective in improving thermal degradation resistivity. The best ionic conductivity of the polymer composite membranes was exhibited at 5.04 × 10−3 S cm−1 using the optimal weight ratio of EVOH/PBT composite controlled at 1/2. On the other hand, the EC/DMC immersion time was more effective in controlling the Rb value, thus the ionic conductivity of the membranes. A higher immersion time, such as 48 h, not only gave higher conductivity data but also provided more stable results. The triallylamine crosslinking agent improved the membrane ionic conductivity by about 22%.

Safe gel polymer electrolytes for high voltage Li-batteries

Gel polymer electrolytes (GPEs), based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), 1 M LiPF6 in ethylene carbonate/dimethyl carbonate (EC/DMC), so called LP30, and 1‑butyl‑1-methylpyrrolidinium hexafluorophosphate ([Py14]PF6), have been developed to improve inherent safety of the electrolyte for high voltage lithium batteries. Dry PVdF-HFP membranes, prepared with EC/DMC, were soaked in LP30 in addition to its mixtures with 30 wt% and 50 wt% [Py14]PF6 to obtain GPEs. Non-flammable character and mechanical stability enhanced via physical crosslinks of the GPEs are demonstrated with flammability tests and rheological measurements, respectively. Lithium ion conduction property in the GPEs is evaluated by means of both electrochemical impedance spectroscopy and NMR spectroscopy (Pulsed Field Gradient-PFG and relaxation time). Galvanostatic charge and discharge cycles of lithium metal batteries having LiNi0.5Mn1.5O4 as a high voltage cathode demonstrate improved electrochemical performance with coulombic efficiency above 99% and high specific capacity above 110 mAh g − 1 at C/5 throughout 150 cycles, when the GPE containing LP30 with 30 wt% [Py14]PF6 is used. The capacity retention is sufficiently high compared to the GPE without [Py14]PF6, confirming that the IL is a highly promising additive for improving battery life.

Influence of a Liquid Electrolyte on Electronic and Ionic Transfers in a LiNi0.5Mn0.3Co0.2O2/Poly(vinylidene Fluoride-co-hexafluoropropylene)-Based Composite Material

The permittivity and conductivity of a porous composite consisting of a mixture of a lithium-ion battery electrode material, LiNi0.5Mn0.3Co0.2O2 (NMC532), and a polymeric binder, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), were simultaneously measured by broadband dielectric spectroscopy (BDS). The composite was either dry or wetted with a conventional battery electrolyte [LP30, LiPF6 in ethylene carbonate/dimethylcarbonate (EC/DMC)] or a mixture of electrolytic solvents (EC/DMC). The experimental results show that the electronic conductivity of NMC532 was much higher than that obtained with LiNi0.33Mn0.33Co0.33O2 (NMC333). In addition, a strong influence of liquids was evidenced. Dipolar species (in particular, EC dipoles) and ions (in particular, PF6– in LP30) considerably increased the surface conductivity of NMC532 clusters, leading to a facilitated electronic transfer from one cluster to another. The effective ionic conductivity was measured and compared to the ionic conductivity of the electrolyte to express the tortuosity factor of this composite electrode.

Molecular Dynamics Simulation of Solvation Nanostructure in Carbonate-Based Electrolyte of Lithium–Sulfur Battery

Lithium–sulfur (Li–S) batteries are widely regarded as the most promising batteries for the future due to their higher specific capacity and lower prices. Various strategies are utilized to alleviate the shortcomings of Li–S batteries failing to reach theoretical capacity. However, basic research at the molecular level continues to be lacking. Therefore, we use molecular dynamics to study the details of the solvated structure of Li–S batteries electrolyte and the nature of the transport process, revealing the relationship between the solvated structure of the electrolyte of LiPF6 and the organic solvent ethylene carbonate/dimethyl carbonate (EC/DMC). The electrolyte of Li2S4 was first simulated in a pure solvent environment. Then the LiPF6 salt was added to the model to simulate a typical electrolyte for a working Li–S battery. Regarding the rationality of the solvent system, various reference systems such as density, dielectric constant, viscosity and diffusion coefficient of the solvent were used for verification. And the detailed composition of the first solvation shell of the polysulfate ion and the coordination number of the ions are discussed. These results provide new insights into the use of EC/DMC electrolytes in Li–S batteries, while at the same time providing a basis for efficient future predictions of electrolyte structure and transport in complex electrode confinements.

Solid electrolyte interphase layer formation on mesophase graphite electrodes with different electrolytes studied by small‐angle neutron scattering

AbstractRelative solid electrolyte interphase (SEI) film thickness investigation on graphite electrodes after the first charge state in the lithium‐ion battery was successfully demonstrated by the ex‐situ small‐angle neutron scattering technique. Here, for both the mesophase graphite powder (MGP) and the fine‐mesophase graphite powder (FMGP) anodes, with two different particle sizes was analyzed precisely by the Guinier–Porod model. The data revealed a stable, maximum (~tens of nm) bi‐layer SEI film formed on MGP anode in ethylene‐carbonate/dimethyl‐carbonate (EC/DMC) at a capacity of 50 mAh/g and sluggish above 100 mAhg‐1. The SEI formed on FMGP with and without 3 wt% fluoroethylene‐carbonate additive in EC/DMC showed the relative thickness greater than that only in ethylene‐carbonate/diethyl‐carbonate. Lithiation initiated the rapid SEI formation on the graphite surface and achieved a maximum thickness in the cell potential ≤0.2 V, and became thinner when the graphite particle expanded after Li+ intercalation. It was observed that the SEI thickness influenced the electrolytes and additives, which might ultimately impact battery performance. Our preliminary results make evident that small‐angle neutron scattering could be employed to better understand the complex microstructure solid electrolyte interphase formation and its accurate thickness, on a mesophase graphite anode.

Interaction between Electrolytes and Sb2O3‐Based Electrodes in Sodium Batteries: Uncovering the Detrimental Effects of Diglyme

AbstractConversion materials are promising to improve the energy density of sodium‐ion‐batteries (NIB). Nevertheless, they suffer from the drawback of phase transitions and pronounced volume changes during cycling, which causes cell instability. When using these types of electrodes, all cell‐components have to be adjusted. In this study, a tremendous influence of the electrolyte solution on Sb2O3 conversion electrodes for NIBs is discussed. Solutions based on three solvents and solvent combinations established for NIBs, ethylene carbonate/dimethyl carbonate (EC/DMC), EC/DMC+5 % fluoroethylene carbonate (FEC), and diglyme, lead to a massively divergent electrochemical behavior of the same Sb2O3 electrode. Sb2O3 demonstrates the highest stability in solutions containing FEC, because this component forms a flexible, protecting surface film that prevent disintegration. One key finding of this work is that electrolyte solutions based on ether solvents like diglyme can remove Sb‐ions from Sb2O3 during cycling. Diglyme has the ability to coordinate and extract Sb3+ during the oxidation of Sb2O3. This leads to contaminations of all cell components and a strong capacity loss together with an irregular electrochemical signature. Due to its poor reactivity at low potentials, diglyme forms a thin or even no surface layer. Thereby, there are no protecting films on the Sb2O3 electrodes that can avoid Sb3+ ion dissolution. A critical examination of the electrolyte solutions components’ impact is essential to match them with conversion reaction anodes.

Scalable and controllable synthesis of 2D high-proportion 1T-phase MoS2

Two-dimensional molybdenum disulfide (2D MoS2) is considered as a promising candidate for many applications due to its unique structure and properties. However, the controllable synthesis of large-scale and high-quality 2D 1T-phase MoS2 is still a challenge. Herein, we present the scalable and controllable synthesis of 2D MoS2 from 2H to 1T@2H phase by using K2SO4 salt as a simultaneous high-temperature sulfur source and template. The as-synthesized 1T@2H-2D MoS2 exhibits a high yield and can be easily assembled into freestanding electrode with high specific capacitance of 434 F/g at a scan rate of 1 mV/s in LiClO4 ethylene carbonate/dimethyl carbonate (EC/DMC). Moreover, various single-crystal 2D transition metal sulfides (WS2, PbS, MnS and Ni9S8) and 2D S-doped carbon can be synthesized using this method. We believe that this study may provide a new sight for scalable and controllable synthesis of other 2D materials beyond 2D MoS2.

Operando Tracking of Solution-Phase Concentration Profiles in Li-Ion Battery Positive Electrodes Using X-ray Fluorescence.

The trade-off between energy density and power capabilities is a challenge for Li-ion battery design as it highly depends on the complex porous structures that holds the liquid electrolyte. Specifically, mass-transport limitations lead to large concentration gradients in the solution-phase and subsequently to crippling overpotentials. The direct study of these solution-phase concentration profiles in Li-ion battery positive electrodes has been elusive, in part because they are shielded by an opaque and paramagnetic matrix. Herein we present a new methodology employing synchrotron hard X-ray fluorescence to observe the concentration gradient formation within Li-ion battery electrodes in operando. This methodology is substantiated with data collected on a model LiFePO4/Li cell using a 1 M LiAsF6 in 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) electrolyte under galvanostatic and intermittent charge profiles. As such, the technique holds great promise for optimization of new composite electrodes and for numerical model validation.

Enhanced safety and galvanostatic performance of high voltage lithium batteries by using ionic liquids

We demonstrate that the addition of 1-butyl-1-methylpyrrolidinium hexafluorophosphate ([Py14]PF6) to 1.0 M LiPF6 in ethylene carbonate-dimethyl carbonate (LP30) widens the temperature range, in which the electrolyte mixtures are ion conductive and safe. Specifically, at the concentrations of [Py14]PF6 above 50 wt%, the electrolyte mixtures exhibit a flash point higher than room temperature and fulfill the requirements of liquids having controlled flammability. In this concentration range, also crystallization of the mixtures is completely suppressed, and low temperature ionic conductivity is improved. With respect to the electrochemical properties at room temperature, electrochemical stability window is widened by the addition of [Py14]PF6 to LP30. However, it comes at the cost of slightly increased overall impedance and overpotential in Li | Li symmetric cells. We utilize these mixed electrolytes in high voltage Li | LiNi0.5Mn1.5O4 cells. In the presence of 30 wt% and 50 wt% of [Py14]PF6 in LP30, the cells exhibit high specific capacity of about 110 mAh g−1 over 200 cycles and improved coulombic efficiency, suggesting [Py14]PF6 is a promising additive for the electrolyte in high-voltage, stable and safe lithium batteries.

Operando Investigation into Dynamic Evolution of Cathode-Electrolyte Interfaces in a Li-Ion Battery.

While Li-ion battery cathode-electrolyte interfaces (CEIs) have been extensively investigated in recent decades, accurately identifying the chemical nature and tracking the dynamics of the CEIs during electrochemical cycling still remain a grand challenge. Here we report our findings in the investigation into the dynamic evolution of the interface between a LiNi0.33Co0.33Mn0.33O2 (LNMC) cathode and an ethylene carbonate/dimethyl carbonate (EC/DMC)-based electrolyte using surface-enhanced Raman spectroscopy (SERS) performed on a model cell under typical battery operating conditions. In particular, the strong SERS activity provided by a monolayer of Au nanocubes deposited on a model LNMC electrode (additive-free) enables quasi-quantitative assessment of the CEI evolution during cycling, proving information vital to revealing the dynamics of the species adsorbed on the LNMC surface as a function of cell potential. Furthermore, our theoretical calculation, which is based on the interaction between a model interface-bound molecule and a model LNMC surface, agrees with our experimental observation. The carefully designed operando SERS platform has demonstrated high sensitivity, good surface specificity, and excellent compatibility with extensive electrochemical measurements; it is also applicable to fundamental studies of dynamic interfaces in other electrochemical energy storage and conversion systems.

Synthesis and characterization of UV-curedpoly(siloxane-urethane) elastomers containing ­polyethylene oxide segments – as potential membrane materials

Conductive polymeric membranes based on poly(siloxane-urethane)s (PSUR) and designed for potential application as separators in Li-ion batteries were obtained through consecutive heat and UV curing of compositions containing NCO-terminated PSUR prepolymers with both polysiloxane (SIL) and poly(ethylene oxide) (PEO) segments in the polymer chain and unsaturated diols as chain extenders. Lithium salts in the form of solutions in ethylene carbonate/dimethyl carbonate (EC/DMC) mixture were incorporated into PSUR after curing (“post-cure” method) or (in some experiments only) also before curing (in situ method). The effect of polymer structural parameters (PEO segments content, NCO/OH ratio) as well as curing conditions and method of lithium salt incorporation on mechanical and thermal properties, swelling ability and specific conductivity of the corresponding membranes were investigated. Supramolecular structure of membranes was studied using scanning electron microscopy with X-ray analysis (SEM/EDS) technique. The selected membranes were tested as potential separators in lithium batteries.

Boron Trifluoride Anionic Side Groups in Polyphosphazene Based Polymer Electrolyte with Enhanced Interfacial Stability in Lithium Batteries.

A modified polyphosphazene was synthesized using a mixed substitution at phosphorus consisting of 2-(2-methoxyethoxy)ethoxy side groups and anionic trifluoroborate groups. The primary goal was to increase the low lithium ion conductivities of the conventional lithium salt containing poly[2-(2-methoxyethoxy)ethoxy-phosphazene] (MEEP) by the immobilized anionic groups. As in previous studies, the mechanical stability was stabilized by UV induced radiation cross linking. By variation of the molar ratio between different side groups, mechanical and electrochemical properties are controllable. The polymer demonstrated large electrochemical stability windows ranging between 0 and 4.5 V versus the Li/Li+ reference. Total and lithium conductivities of 3.6 × 10−4 S·cm−1 and 1.8 × 10−5 S·cm−1 at 60 °C were revealed for the modified MEEP. When observed in special visualization cells, dendrite formation onset time and short-circuit time were determined as 21 h and 90 h, respectively, under constant current polarization (16 h and 65 h for MEEP, both with 15 wt % LiBOB), which hints to a more stable Li/polymer interface compared to normal MEEP. The enhanced dendrite suppression ability can be explained by the formation of a more conductive solid electrolyte interphase (SEI) and the existence of F-contained SEI components (such as LiF). With the addition of ethylene carbonate–dimethyl carbonate (EC/DMC) to form MEE-co-OBF3P gel polymer, both total and lithium conductivity were enhanced remarkably, and the lithium transference numbers reached reasonable values (σtotal = 1.05 mS·cm−1, σLi+ = 0.22 mS·cm−1, = 0.18 at 60 °C).

Bombyx mori Silkworm Cocoon Separators for Lithium‐Ion Batteries with Superior Safety and Sustainability

AbstractIn the quest for solutions to enhance the safety and sustainability of energy storage devices, Bombyx mori silkworm cocoons are proposed as separators for lithium (Li)‐ion batteries obtained literally from nature, and employed directly in a device. The suitability of the cocoons is evaluated in Li‐ion batteries using two different electrolytes: a mixture of lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), and dimethyl carbonate (DMC), and the ionic liquid (IL) 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim]TFSI). Li/C–LiFePO4 half cells comprising the EC–DMC–LiPF6 electrolyte present excellent cycling performance, with a discharge capacity up to 86 mAh g−1 and a capacity retention up to 81% after 50 cycles at C rate. Values of 66 mAh g−1 at C/5 and 85% result with [Emim]TFSI, respectively. Separator/electrolyte interactions during battery cycling lead to a decrease of the degree of crystallinity of the cocoon silk fibers, and, in the presence of EC–DMC–LiPF6, to a concomitant increase of the concentration of free PF6− ions. The self‐extinguishing ability of silkworm cocoons represents an additional benefit to batteries, providing fire risk reduction or even suppression. This bio‐inspired work paves the way toward the fabrication of environmentally friendlier separators for next‐generation sustainable and safer Li‐ion batteries.

New Insight for Surface Chemistries in Ultra-thin Self-assembled Monolayers Modified High-voltage Spinel Cathodes

The electrochemical properties of the interface between the spinel LiNi0.5Mn1.5O4-δ (LNMO4-δ) cathodes and ethylene carbonate−dimethyl carbonate (EC-DMC) electrolyte containing 1 M of LiPF6 have been investigated to achieve high-voltage durability of LNMO4-δ/graphite full cells. Coating the LNMO4-δ crystal surface by a fluoroalkylsilane self-assembled monolayer with a thickness below 2 nm resulted in a capacity retention of 94% after 100 cycles at a rate of 1 C and suppression of capacity fading for both the cathode and anode of the full cell. The observed effect is likely caused by the inhibited oxidative decomposition of EC−DMC electrolyte and vinylene carbonate (VC) species at the LNMO4-δ crystal surface and formation of a stable VC solid electrolyte interface near the anode. Moreover, the results obtained via photoelectron spectroscopy and density-functional calculations revealed that the increase in the work function of the LNMO4-δ crystal surface due to the formation of Si−O−Mn species primary contributed to the inhibition of the oxidative decomposition of the electrolyte and VC molecules at the cathode/electrolyte interface.