Electrolytes For Lithium Batteries Research Articles

Electrochemical study comparing liquid and gel electrolytes for lithium-ion batteries based on LiTDI or LiPF6

Electrochemical study comparing liquid and gel electrolytes for lithium-ion batteries based on LiTDI or LiPF6

SEI-Coated Carbon Particles: Electrochemomechanical Fracture Mechanisms

By starting from fundamental physical principles, a generalized theoretical framework was developed to engineer the intercalation-induced mechanical degradation in SEI-coated carbon particles from the surrounding electrolyte in rechargeable lithium-ion batteries (LIBs). Six elemental regimes of fracture formation in spherical electrochemically active carbon particles of radius, r p , coated with an SEI layer of thickness, δ ≪ r p , have been identified: The pristine regime, the SEI debonding regime, the SEI surface flaw regime, the surface carbon flaw regime (delithiation), the internal circular carbon flaw regime (lithiation), and the carbon exfoliation regime (lithiation); as well as four combined regimes during delithiation and four combined regimes during lithiation. Results are summarized in terms of C-Rate versus particle size, degradation maps, to identify LIB operation conditions where the performance can be optimized, while suppressing the decrepitation of the SEI-coated carbon particle system. Improved porous electrode layers that deliver longer battery life are possible by selecting electrolytes that considering the design of SEI-coated carbon particles of tailored elastic stiffness and critical stress intensity factor, so that they are safe from developing a chemomechanically induced flaw, exfoliation, or carbon re-forming, during both lithiation or delithiation in the 1 to 10 μm size particle, and C-Rates < 1 C.

H2O/HF Scavenging Mechanism in Cellulose-Based Separators for Lithium-Ion Batteries with Enhanced Cycle Life.

Lithium-ion batteries (LIBs) are increasingly being integrated into the transportation industry due to their high energy density, durability, and low cost. With the growing demand for transportation and other emerging applications, there is a concurrent rise in concern over LIB material sourcing and recycling. This urges the development of LIBs with extended cycle lifespans. One mechanism of capacity fading in LIBs is the dissolution of transition metals into the electrolyte after the cathode is etched with hydrofluoric acid (HF). HF is readily generated by the hydrolysis of the LIB electrolyte salt, lithium hexafluorophosphate (LiPF6), which makes minimizing moisture in the electrolyte a priority in manufacturing. In this study, a nonwoven, cellulose-based separator (CBS) is introduced as an alternative separator for battery technologies to scavenge residual water and HF from the electrolyte. The CBS is shown to be capable of scavenging varying amounts of water from the electrolyte based on different drying processes of the CBS, and a mechanism for this water scavenging is identified based on the materials present in the CBS. In addition, the chemical and electrochemical performance of the CBS in real battery conditions is investigated. Results suggest an effective H2O/HF scavenging capability in the CBS that allows LIB coin cells to have over 17% higher capacity retention than those with conventional separators. Furthermore, studies of the industrially manufactured, commercially relevant cylindrical and pouch cells show remarkable 761 and 103% improvements in the 60% capacity lifetime, respectively. The environmental friendliness, low cost, and easy application empowered by the cycle life improvements shown in this work make this nonwoven CBS a promising candidate for improving industry-level LIB performance.

Fluorine-Terminated Self-Assembled Monolayers Grafted Graphite Anode Inducing a LiF-Dominated SEI Inorganic Layer for Fast-Charging Lithium-Ion Batteries.

The electrochemical kinetic processes of Li+ ions, including the desolvation of the Li+ ions from the electrolyte to the solid electrolyte interphase (SEI), the transportation of desolvated Li+ ions across the SEI, and the charge transfer at the interface between the SEI and graphite, determine the rate performance and cycling stability of the graphitic anode in lithium-ion batteries (LIBs). In this work, fluorine-terminated self-assembled monolayers were grafted on the surface of spherical graphite particles to regulate the chemical composition and structure of SEI formed on the graphite surface in the presence of conventional ester electrolytes. The comprehensive characterization and first-principles calculation results illustrate that a uniform LiF-dominated SEI film can be generated on the as-functionalized graphite anode due to the carbon-fluorine bonds' cleavage of fluorine-terminated self-assembled monolayers. The LiF-dominated SEI film is particularly beneficial for desolvated lithium-ion transport across the SEI, affording LiCoO2//graphite full cells with substantially enhanced fast-charging capability and cycle stability. This strategy should be potentially useful for modifying other anode materials to regulate the interfacial chemistry between the anode and electrolyte in lithium-ion batteries.

Remarkably improved ionic conductivity and lithium metal compatibility of LLZTO-Li4(BH4)3I composite solid-state electrolyte

With superior ionic conductivity and (electro)chemical stability, garnet-type oxide Li6.4La3Zr1.4Ta0.6O12 (LLZTO) has been extensively studied and explored as advanced solid-state electrolyte (SSEs) for lithium ion batteries (LIBs). However, high-temperature sintering treatment at ∼1200 °C to fabricate dense sheets is necessary to attain high ionic conductivity, whereas at the expense of degraded mechanical properties and poor contact with electrodes. Herein, we demonstrate a novel LLZTO-Li4(BH4)3I composite solid electrolyte prepared by mechanical milling, which features a bilayer coating structure where LiBO2 in the inner layer and Li4(BH4)3I in the outer layer. The electrolyte pellets fabricated by a simple cold pressing treatment deliver an ionic conductivity of 3.69 × 10−5 S cm−1 at 30 °C and a Li+ transference number of 0.9999, which successfully prevents the formation of lithium dendrites. Using this electrolyte, Li|Li symmetric batteries can work continuously for more than 2200 h at 35 and 60 °C. Such performance improvement is ascribed to the sharp reduction in porosity, the enhanced mechanical properties and the improved interface contact after cold pressing the Li4(BH4)3I-modified LLZTO composite to form an electrolyte pellet.

Enhancing the performance of metallic lithium anode in batteries through water-resistant and air-stable coating

The limited reversibility and high reactivity of lithium metal with the liquid electrolyte in lithium batteries hinder its widespread adoption. The formation of an unstable solid electrolyte interphase layer and the sensitivity of lithium metal to moisture and air are major issues that need to be addressed. To overcome the practical challenges associated with the application of lithium anodes in lithium metal batteries, a well-thought-out design of a protective layer is proposed. Here, we have developed a composite coating comprising polyvinylidene fluoride, fumed colloidal silica, and paraffin wax as a protective layer for lithium metal anodes. The coating exhibits excellent electrochemical stability, high ionic conductivity, and mechanical stability, effectively suppressing dendrite growth and accommodating lithium volume changes during cycling. Moreover, the hydrophobic wax component can mitigate the atmospheric sensitivity of metallic lithium anodes. The coating process employed is facile and economically viable, significantly enhancing the scalability of lithium metal batteries. Experimental characterizations confirm the structure and composition of the coating, and electrochemical measurements demonstrate the improved electrochemical performance and cyclability of the coated lithium metal anodes. The results indicate that the developed composite coating has great potential for enhancing the electrochemical and processing stability of metallic lithium anodes for lithium metal batteries.

Experimental and modeling study on ignition kinetics of ethyl methyl carbonate

Ethyl methyl carbonate (EMC) is an essential electrolyte of lithium-ion batteries (LIBs), and the spontaneous ignition of electrolyte is considered to be an important inducement for the thermal runaway (TR) combustion of LIBs. To better understand its ignition chemistry and combustion kinetics, the ignition delay times (IDTs) of ethyl methyl carbonate were measured by using a Rapid Compression Machine (RCM) over a wide range of temperatures (810–980 K), pressures (20 and 40 bar), equivalence ratios (φ = 0.5, 1.0, and 2.0), and a fuel concentration of 2 %, yielding results that are in substantial variance with those calculated with detailed kinetics in the literature over the entire range of conditions investigated. An improved chemical kinetic model was developed to simulate the ignition and combustion characteristics of EMC under intermediate-temperature region by employing the updated kinetic parameters. Results show that the overall performance of the present kinetics model is substantially improved with respected to the prediction of ignition delay times, intermediate species profiles, as well as laminar flame speeds across different temperature, pressure, and equivalence ratio conditions. Furthermore, sensitivity and pathway analyses show that the ignition chemistry of EMC is mainly controlled by retro-ene reaction and H abstraction reactions.

A novel hyperbranched polyurethane solid electrolyte for room temperature ultra-long cycling lithium-ion batteries

Low room temperature ionic conductivity of solid polymer electrolytes (SPE) greatly constraints its application in the solid lithium-ion batteries. Hyperbranched polymer with unique topological structure as matrix of SPE is expected to solve this issue due to its low crystallinity and rich functional groups which helps dissociation of lithium salt. Herein, a hyperbranched polyurethane (HPU) solid electrolyte is prepared by the reaction of hyperbranched polyethylene glycol and isophoradione diisocyanate in the presence of lithium salt and ionic liquid for the first time. The obtained HPU1.5-IL1.5 electrolyte possesses a high room temperature ionic conductivity of 0.4 mS cm−1 and a wide electrochemical window of 4.95 V (vs Li/Li+). It is worth noting that the prepared HPU1.5-IL1.5 electrolyte can be adapted to multiple electrodes. Specifically, the assembled LFP half-cell can achieve long cycling up to 1000 cycles at 0.5 C with 83 % capacity retention at room temperature. Notably, the NCM811|HPU1.5-IL1.5|Li cells and LTO|HPU1.5-IL1.5|Li cells can deliver the initial discharge capacity of 148 mAh g−1 at 0.1 C for 160 cycles and the initial discharge capacity of 150 mAh g−1 at 0.2 C for 440 cycles at room temperature, respectively. Meanwhile, the safety of the pouch cell has been confirmed under some extreme conditions.

Polyethylene Oxide-Based Composite Solid Electrolytes for Lithium Batteries: Current Progress, Low-Temperature and High-Voltage Limitations, and Prospects

Polyethylene Oxide-Based Composite Solid Electrolytes for Lithium Batteries: Current Progress, Low-Temperature and High-Voltage Limitations, and Prospects

Preparation and characterization of hybrid solid-state electrolytes for high performance lithium-ion batteries

Hybrid solid-state electrolytes are emerging as a promising solution to achieve high ionic conductivity, excellent mechanical properties and good safety for developing high-performance rechargeable batteries. In this work, a polymer (PAN)-based hybrid solid-state electrolyte is designed and synthesized. The composite membrane (PLL) is composed of polyacrylonitrile (PAN) matrix, bistrifluoromethanesulfonimide lithium salt (LiTFSI) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) particles. The solid-state lithium battery including the as-synthesized composite membrane, Li metal and LiNi0.8Co0.1Mn0.1O2 exhibits an initial discharge capacity of 197 mAh g−1 at a charge/discharge current density of 0.5 C at room temperature. The battery using the PLL-20 electrolyte exhibits the highest stable cycling performance and highest reversible capability than those of the batteries with PLL-10, PLL-30 membrane electrolytes and commercial PE separator, respectively.

Trifluoromethylated Lithium Borates as Electrolyte Salts for High‐Energy‐Density Lithium‐Ion Batteries with High‐Voltage LiNi0.5Mn1.5O4 Positive Electrodes

AbstractLiNi0.5Mn1.5O4 (LNMO) is a promising positive electrode material for high‐energy‐density lithium‐ion batteries (LIBs) because of its high working voltage; however, its practical application is hindered by the insufficient oxidation resistance of LIB electrolytes. In this study, we aimed to address this issue by evaluating two trifluoromethylated lithium borate compounds lithium difluoro (perfluoropinacolato) borate (PFP‐F2) and lithium difluoro(2‐hydroxy‐3,3,3,3′,3′,3′‐hexafluoroisobutylato) borate (HHIB‐F2) as electrolyte salts for high‐potential LIBs (4.8 V vs. Li/Li+) with LNMO positive electrodes. In full‐cell tests, the cyclability of LIBs containing these salts is superior (60 °C) to that of the cell with lithium tetrafluoroborate (LiBF4) as the reference electrolyte salt, which is ascribed to the formation of a positive electrode passivation layer that inhibits the oxidative decomposition of the electrolyte salt and solvent in the former case. Moreover, the oxidative decomposition of trifluoromethylated borates at 4.8 V affords a passivation layer on the negative electrode. Thus, the examined borates hold great promise for the commercialization of high‐energy‐density LNMO‐based LIBs, and the formation of a solid electrolyte interphase (SEI) at the negative electrode resulting from the oxidative decomposition products of electrolyte salts is a promising new way to enhance the performance of high‐potential positive electrode LIBs beyond existing levels.

Effect of Sr and Ta co-substitution on microstructure and ionic conductivity of cubic-Li0.5La0.5TiO3 electrolyte for applications in Li batteries

All-solid-state lithium batteries (ASSBs) have gained significant attention in recent years because of their potential to offer higher energy density and enhanced safety compared to conventional liquid-electrolyte-based lithium-ion batteries (LIBs). Lithium lanthanum titanate (LLTO) is a promising solid electrolyte for next-generation lithium batteries owing to its high ionic conductivity of approximately 10−3 S·cm−1 at room temperature (RT). The Sr and Ta co-doped Li0.5-□La0.5−xSrxTi1−xTaxO3 perovskites were synthesized by solid-state reaction. In this study, Sr2+ and Ta5+ with larger ionic radii, were used for co-substitution in the La3+ and Ti4+ sites, respectively, to increase the bottleneck size of the A-site and expand the average bond length of the B-site on the perovskite structure (ABO3), thereby increasing the Li+ ion mobility. The LLSrxTTaxO3 (0 ≤ x ≤ 0.12) pellets have high relative densities, and high grain conductivities, where the total conductivity of LLSr0.09TTa0.09O3 reached 4.12 × 10−5 S·cm−1. Compared with the pure specimen, the total conductivities of the doped specimens are approximately more than 2.7 times at RT. The assembled semi-solid LFP/10 wt% LLSr0.09TTa0.09O3/Li full battery has a 0.1 C specific discharge capacity of 156 mAh⋅g−1 and a 1 C capacity retention rate of 86% after 290 cycles at RT.

Facile Route to Synthesize a Highly Sinterable Li1.3Al0.3Ti1.7(PO4)3 Solid Electrolyte.

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a widely used solid electrolyte in solid-state lithium batteries, owing to its excellent chemical stability against moisture and high total ionic conductivity. However, traditionally, densification of LATP has been achieved through a high-temperature sintering process (approximately 1000 °C) owing to its poor sinterability. Herein, we report a facile synthesis route to obtain highly sinterable LATP solid electrolyte using tetrabutyl titanate (C16H36O4Ti) as the titanium source and incorporating the traditional solid-state reaction method. The synthetic LATP powder mixed with a low ratio of LiTiPO5 exhibited a hybrid crystalline-amorphous phase structure, which facilitated grain fusion, promoted structural homogeneity, and facilitated structural densification under low-temperature sintering. The sintered LATP pellet, which exhibited an interconnected structure and indistinct grain boundaries, achieved a relative density of >90% and an ionic conductivity of 0.667 mS/cm at a sintering temperature of only 750 °C. Additionally, we systematically studied and demonstrated the synthesis reaction mechanism, sintering behavior, and ionic diffusion kinetics of LATP electrolytes. Our study paves the way for synthesizing highly sinterable LATP solid electrolytes using a simple, additive-free, and cost-effective method.

A strong nucleophilic fluorination agent to achieve highly stable in-situ 3D cross-linked gel polymer electrolyte for lithium-ion batteries

The Gel Polymer Electrolyte (GPE) is recognized as a promising alternative to conventional electrolytes, aiming to enhance the longevity and energy density of lithium-ion batteries (LIBs). However, several challenges persist, particularly concerning the conductivity and voltage window of GPE in battery systems. In this study, we introduce an in-situ 3D crosslinked GPE, using polymethyl methacrylate (PMMA) as the monomer and polyethylene glycol dimethacrylate (PEGDMA) as the crosslinking agent, to ensure structural stability and optimized ion conductivity. We also incorporate a potent nucleophilic fluorination agent, Tetrabutylammonium fluoride (TBAF), to augment the compatibility and oxidation resistance of the formulated FGPPE. The recurring (–CH2CH2O-) units of PEGDMA, coupled with in-situ lithium fluoride (LiF) and C-F groups introduced by TBAF, endow the FGPPE with a remarkable ionic conductivity of 7.8 mS cm−1 and a distinctly electrochemical stability of 4.65 V. Notably, the Li metal anode, featuring an F-rich solid-state interface (SEI), demonstrates uniform Li+ deposition, sustaining a cycling life of 1000 h and maintaining a commendable average coulomb efficiency of 98.5 % over 300 cycles. Additionally, the NCM811/SiC pouch cell integrated with FGPPE showcases superior cycling stability, retaining 99.4 % of its capacity after 600 cycles at an elevated voltage of 4.45 V. Such advancements in gel polymer electrolyte design can significantly expedite the commercial deployment of gel polymer Li-ion batteries.

A Critical Analysis of Chemical and Electrochemical Oxidation Mechanisms in Li-Ion Batteries.

Electrolyte decomposition limits the lifetime of commercial lithium-ion batteries (LIBs) and slows the adoption of next-generation energy storage technologies. A fundamental understanding of electrolyte degradation is critical to rationally design stable and energy-dense LIBs. To date, most explanations for electrolyte decomposition at LIB positive electrodes have relied on ethylene carbonate (EC) being chemically oxidized by evolved singlet oxygen (1O2) or electrochemically oxidized. In this work, we apply density functional theory to assess the feasibility of these mechanisms. We find that electrochemical oxidation is unfavorable at any potential reached during normal LIB operation, and we predict that previously reported reactions between the EC and 1O2 are kinetically limited at room temperature. Our calculations suggest an alternative mechanism in which EC reacts with superoxide (O2-) and/or peroxide (O22-) anions. This work provides a new perspective on LIB electrolyte decomposition and motivates further studies to understand the reactivity at positive electrodes.

Crosslinked Gel Polymer Electrolyte from Trimethylolpropane Triglycidyl Ether by In Situ Polymerization for Lithium-Ion Batteries.

Electrolytes play a critical role in battery performance. They are associated with an increased risk of safety issues. The main challenge faced by many researchers is how to balance the physical and electrical properties of electrolytes. Gel polymer electrolytes (GPEs) have received increasing attention due to their satisfactory properties of ionic conductivity, mechanical stability, and safety. Herein, we develop a gel network polymer electrolyte (GNPE) to address the challenge mentioned earlier. This GNPE was formed by tri-epoxide monomer and bis(fluorosulfonyl)imide lithium salt (LiFSI) via an in situ cationic polymerization under mild thermal conditions. The obtained GNPE exhibited a relatively high ionic conductivity (σ) of 2.63 × 10-4 S cm-1, lithium transference number (tLi+, 0.58) at room temperature (RT), and intimate electrode compatibility with LiFePO4 and graphite. The LiFePO4/GNPE/graphite battery also showed a promising cyclic performance at RT, e.g., a suitable discharge specific capacity of 127 mAh g-1 and a high Coulombic efficiency (>97%) after 100 cycles at 0.2 C. Moreover, electrolyte films showed good mechanical stability and formed the SEI layer on the graphite anode. This study provides a facile method for preparing epoxy-based electrolytes for high-performance lithium-ion batteries (LIBs).

Solid-state polymer electrolytes in lithium batteries: latest progress and perspective

This review provides a comprehensive overview of solid-state polymer electrolytes performance characteristics of various chemical structures such as ethers, esters, nitrile and vinylidene fluoride.

Atomistic origin of high grain boundary resistance in solid electrolyte lanthanum lithium titanate

Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to ∼10−3 S/cm. However, the practical application of this material has been bottlenecked by high grain boundary (GB) resistance, while the underlying mechanism is still under debate. Here we report a comprehensive study with direct evidence to reveal the origin of high GB resistance in La2/3–xLi3xTiO3 (LLTO). Atomic-scale observations via advanced scanning transmission electron microscopy show that the GBs are uniformly subject to subsurface segregation of La atoms to compensate for the excess surface charges. The La segregation leads to an abrupt decrease of charge carrier concentration neighboring GBs and hence is supposed to have deleterious effect on GB conductivity. The findings suggest a novel mechanism of space-charge-induced cation segregation, which shed lights on the intrinsic origin of low GB ionic conductivity in LLTO.

Recent progress and perspectives on metal-organic frameworks as solid-state electrolytes for lithium batteries.

Solid-state electrolytes (SSEs) are the key materials in the new generation of all-solid-state lithium ion/metal batteries. Metal-organic frameworks (MOFs) are ideal materials for developing solid electrolytes because of their structural diversity and porous properties. However, there are several significant issues and obstacles involved, such as lower ion conductivity, a smaller ion transport number, a narrower electrochemical stability window and poor interface contact. In this review, a comprehensive analysis and summary of the unique ion-conducting behavior of MOF-based electrolytes in rechargeable batteries are presented, and the different design principles of MOF-based SSEs are classified and emphasized. Accordingly, four design principles for achieving these MOF-based SSEs are presented and the influence of SSEs combined with MOFs on the electrochemical performance of the batteries is described. Finally, the challenges in the application of MOF materials in lithium ion/metal batteries are explored, and directions for future research on MOF-based electrolytes are proposed. This review will deepen the understanding of MOF-based electrolytes and promote the development of high-performance solid-state lithium ion/metal batteries. This review not only provides theoretical guidance for research on new MOF-based SSE systems, but also contributes to further development of MOFs applied to rechargeable batteries.

Formulating compatible non-flammable electrolyte for lithium-ion batteries with ethoxy (pentafluoro) cyclotriphosphazene.

Lithium (Li) ion batteries have played a great role in modern society as being extensively used in commercial electronic products, electric vehicles, and energy storage systems. However, battery safety issues have gained growing concerns as there might be thermal runaway, fire or even explosion under external abuse. To tackle these safety issues, developing non-flammable electrolytes is a promising strategy. However, the balance between the flame-retarding effect and the electrochemical performance of electrolytes remains a great challenge. Herein, we evaluate the function of ethoxy (pentafluoro) cyclotriphosphazene (PFPN) as an effective flame-retarding additive for lithium-ion batteries. The flammability of electrolytes is greatly suppressed with the introduction of a small amount of PFPN. Moreover, PFPN exhibited excellent compatibility with LiFePO4 (LFP) cathode and graphite (Gr) anode, the electrochemical performances of LFP|Li and Gr|Li half cells are virtually unaffected. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) reveal the stable interphase between PFPN-containing electrolyte and LFP and Gr electrodes. Fourier transform infrared spectroscopy (FT-IR), Raman and nuclear magnetic resonance (NMR) spectra demonstrate the introduction of PFPN only exhibits negligible influence on the solvation structure of electrolyte. Benefiting from these merits of PFPN, the LFP|Gr cell shows desirable long-term cycling performance, which demonstrates great potential for practical application.