Electrolytes For Li-ion Batteries Research Articles

Mitigation of grain boundary resistance in La2/3-xLi3xTiO3 perovskite as an electrolyte for solid-state Li-ion batteries

In this work, we report that modification of the chemical composition of grain boundaries of La2/3-xLi3xTiO3 double perovskite, one of the most promising Li-ion conducting solid electrolytes, can be a convenient and versatile way of controlling the space charge potential, leading to a mitigated electrical resistance of the grain boundaries. Two groups of additives are investigated: lithium-enriching agents (Li3BO3, LiF) and 3d metal ions (Co2+, Cu2+), both expected to reduce the Schottky barrier. It is observed that Li-containing additives work effectively at a higher sintering temperature of 1250 °C. Regarding copper, it shows a much stronger positive impact at lower temperature, 1150 °C, while the addition of cobalt is always detrimental. Despite overall complex behavior, it is documented that the decreased space charge potential plays a more important role in the improvement of lithium conduction than the thickness of the grain boundaries. Among the proposed additives, modification of La2/3-xLi3xTiO3 by 2 mol.% Cu2+ results in the space charge potential reduction by 32 mV in relation to the reference sample, and the grain boundary specific conductivity increase by 80%, as measured at 30 °C. Introduced additive allows to obtain a similar effect on the conductivity as elevating the sintering temperature, which can facilitate manufacturing procedure.Graphic abstract

Li4–xGe1–xPxO4, a Potential Solid-State Electrolyte for All-Oxide Microbatteries

Solid-state electrolytes for Li-ion batteries are attracting growing interest as they allow building safer batteries, also using lithium metal anodes. Here we studied a compound in the lithium superionic conductor (LISICON) family, i.e. Li4-xGe1-xPxO4 (LGPO). Thin films were deposited via pulsed laser deposition and their electrical properties were compared with ceramic pellets. A detailed characterization of the micro structure shows that thin films can be deposited fully crystalline at higher temperatures but also partially amorphous at room temperature. The conductivity is not strongly influenced by the presence of grain boundaries, exposure to air or lithium deficiencies. First-principles molecular dynamics simulations were employed to calculate the lithium ion diffusion profile and the conductivity at various temperatures of the ideal LGPO crystal. Simulations gives the upper limit of conductivity for a defect free crystal, which is in the range of 10-2 S cm-1 at 300 deg. The ease of thin film fabrication, the room-temperature Li-ion conductivity in the range of a few microS cm-1 make LGPO a very appealing electrolyte material for thin film all-solid-state all-oxide microbatteries.

Electrochemistry and transport properties of electrolytes modified with ferrocene redox-active ionic liquid additives

Used in their pure, undiluted form, ionic liquids usually result in Li-ion battery electrolytes with inadequate performance due low Li+ transport numbers (tLi+). Alternatively, they can be used as additives dissolved in carbonates to maintain a high tLi+ while providing the electrolyte with additional properties such as resistance to combustion, current collector passivation, and decreased Li dendritic growth. Additional properties can be imparted to the ionic liquid via the modification of their structure. Ionic liquids modified with electroactive moieties such as ferrocene (Fc-IL) can be used as an additive in Li-ion battery (LiB) electrolytes to prevent cathode over-oxidation via the redox shuttle mechanism. The aim of the present work is to evaluate the properties of LiB electrolytes modified with such Fc-IL at different concentrations. At low concentrations (0.3–0.5 mol/L), the redox-active ionic liquid behaves as expected for a redox shuttle. We show that at 1 mol/L, however, the redox ionic liquid yields a different discharge behavior after the overcharging step, providing an increase in discharge capacity. This behavior is linked to the deposition of the ferrocenium-IL at the positive electrode. Such electrolyte is non-flammable and is highly efficient to achieve shuttling of excess charge. Based on this principle, it is expected that novel ionic liquids can be designed for development of other types of additives and contribute to developing safer battery electrolytes. As a part of this commemorative issue, this contribution highlights the type of collaborative research currently being done on energy storage devices at the Department of Chemistry at the Université de Montréal.

Ionic conductivity in LixTaOy thin films grown by atomic layer deposition

The material system Li-Ta-O is a promising candidate for thin-film solid-state electrolytes in Li-ion batteries. In the present study, we have varied the Li content x in LixTaOy thin films grown by atomic layer deposition (ALD) with the aim of improving the Li-ion conductivity. The amorphous films were grown at 225 °C on insulating sapphire and on conductive Ti substrates using tantalum ethoxide (Ta(OEt)5), lithium tert-butoxide (LiOtBu) and water as reactants. The film composition was determined by time-of-flight elastic recoil detection analysis (TOF-ERDA), displaying an almost linear relationship between the pulsed and deposited Li content. The ionic conductivities were determined by in-plane and cross-plane AC measurements, exhibiting an Arrhenius-type behaviour and comparatively weak thickness-dependence. Increasing Li content x from 0.32 to 0.98 increases the film conductivity by two orders of magnitude while higher Li content x = 1.73 results in decreased conductivity. A room-temperature conductivity σRT of ~10−8 S cm−1 is obtained for a 169 nm thick Li0.98TaOy film. The evolution of conductivity and activation energy suggests a competing effect between the concentration and the mobility of mobile Li ions when more Li are incorporated. The compositional dependence of Li transport mechanism is discussed.

Recent Advancements in High-Performance Solid Electrolytes for Li-ion Batteries: Towards a Solid Future

With the emergence of non-conventional energy resources and development of energy storage devices, serious efforts on lithium (Li) based rechargeable solid electrolyte batteries (Li- SEBs) are attaining momentum due to their potential as a safe candidate to replace state-of-the-art conventionally existing flammable organic liquid electrolyte-based Li-ion batteries (LIBs). However, Li-ion conduction in solid electrolytes (SEs) has been one of the major bottlenecks in large scale commercialization of next-generation Li-SEBs. Here, in this review, various challenges in the realization of high-performance Li-SEBs are discussed and recent strategies employed for the development of efficient SEs are reviewed. In addition, special focus is laid on the ionic conductivity enhancement techniques for inorganic (including ceramics, glasses, and glass-ceramics) and polymersbased SEs. The development of novel fabrication routes with controlled parameters and highperformance temperature optimized SEs with stable electrolyte-electrode interfaces are proposed to realize highly efficient Li-SEBs.

Evaluating Solid-Electrolyte Interphases for Lithium and Lithium-free Anodes from Nanoindentation Features

Summary The morphology and mechanical property of SEIs for lithium anodes crucially affect the electrochemical cycling performance of Li-metal batteries such as Li-S and Li-O2 batteries. Herein, we establish the standards for rapidly assessing SEIs for Li and Li-free type of anodes by AFM nanoindentation features toward prediction of corresponding electrochemical performances. A series of single-layered and multi-layered SEIs with known composition and structures are purposely constructed. A set of unique nanoindentation features representative of mechanical properties of the basic SEIs are formed, serving as the standards for rapidly assessing the mechanical properties and electrochemical performances of unknown SEIs together with their Young’s modulus, smoothness, and thickness. To validate the applicability of the method, SEIs formed by electrochemical aging and formed on Cu substrates are further evaluated. Our work not only contributes to understanding the influence of SEIs on cycling performances but also provides a rapid way for screening SEIs.

Inhomogeneous distribution of lithium and electrolyte in aged Li-ion cylindrical cells

Carbonate-based electrolytes in Li-ion batteries exhibit long range order in a frozen state, which enables their non-destructive analysis by diffraction methods. In the current study the spatial distribution of lithium and electrolyte inside the graphite anode was determined in cycled Li-ion cells using monochromatic spatially-resolved neutron diffraction measurements at 150 K. The results indicate a loss of lithium and electrolyte and their non-uniform distribution in the graphite anode in aged Li-ion cells. The observed lithium and electrolyte losses are directly correlated with two electrochemical performance degradation mechanisms, which are responsible for the cell capacity fade.

Effect of salt concentration on properties of mixed carbonate-based electrolyte for Li-ion batteries: a molecular dynamics simulation study.

In this work, a computational framework is proposed by utilizing molecular dynamics simulation to explore the existing relation between molecular structure and ionic conductivity of the electrolyte system [LiPF6+(EC+DMC 1:1)] consisting of a mixture of cyclic ethylene carbonate (EC) and acyclic dimethyl carbonate (DMC) solvents and lithium hexafluorophosphate (LiPF6) salt to propose as a novel mixed organic solvent-based electrolytes to promote the performance of lithium-ion batteries (LIBs). To acquire a clear understanding of the structural and transport properties of the designed electrolytes, quantum chemistry (QC) calculations and molecular dynamics (MD) simulation are used. In the first step, the accurate molecular structures of the studied electrolytes in addition to their corresponding atomic partial charges are evaluated. The MD simulations are performed at 330K varying the LiPF6 concentration (0.5M to 2.2M). Analysis of the obtained results indicated that ionic diffusivity and conductivity of the electrolytes are dependent on the structure of solvated ions and lithium salt (LiPF6) concentration. It is found that the obtained MD simulation results are in reasonable agreement with experimental results. Graphical abstract A representation of dependence of transport properties of electrolyte system [LiPF6 +(EC+DMC 1:1)] as function of salt concentration to be used in Lithium-ion batteries (LIBs).

Understanding the Ionic Diffusivity in the (Meta)Stable (Un)doped Solid-State Electrolyte from First-Principles: A Case Study of LISICON

The solid electrolyte is expected to be an alternative to the liquid electrolyte in Li-ion batteries. The former is believed to be safer, capable of delivering higher energy density, faster recharg...

A novel densification model for sintering Li7La3Zr2O12-based solid electrolytes for all solid-state Li-ion batteries

Improving the safety features of traditional Li-ion batteries having a flammable liquid electrolyte is one of the current challenges that scientists have been trying to overcome. Inorganic solid ionic conductors are promising option to replace the liquid electrolytes in Li-ion batteries because of their high temperature stability. But their poor ionic conductivity is one bottleneck that prevents them in a widespread use. In order to increase the ion conduction, the electrolytes should be as dense as possible since pores have no contribution to ionic conductivity. For densification assessments during sintering of Li7La3Zr2O12, one of the popular inorganic solid ion conductors in the field of all solid-state Li-ion batteries, the Archimedes density measurement technique has been widely used. However, the Archimedes density itself is not sufficient enough to enlighten the densification behavior of Li7La3Zr2O12 since closed porosities that are very common in Li7La3Zr2O12 microstructures cannot be wetted by the immersed liquid. In this study, a densification model which combines Archimedes density with radial shrinkage, dilatometer, and microstructure for more accurate assessment of Li7La3Zr2O12 densification was offered. Optical dilatometer results showed shrinkage initiation after 980 °C. Archimedes densities were initially increased from 4.24 to 4.76 g/cm3 at the early stages of sintering and then stayed constant at 4.76 g/cm3. On the other hand, radial shrinkage showed continual increase from 7.33 to 13.20% pointing out the linking of closed porosities and grain separation.

Recent Advances in Filler Engineering of Polymer Electrolytes for Solid-State Li-Ion Batteries: A Review

Solid-state Li-ion batteries (SSBs) have been regarded as the most promising systems to power electronic devices and electric vehicles because of their high energy density and safety. As the key co...

Electrochemical performance of Li-rich NMC cathode material using ionic liquid based blend polymer electrolyte for rechargeable Li-ion batteries

In this paper, synthesis of lithium rich nickel manganese cobalt oxide cathode material (Li1·2Ni0·6Mn0·1Co0·1O2) and ionic liquid (IL) based blend gel polymer electrolytes (BGPEs) are reported. Li1.2Ni0.6Mn0.1Co0.1O2 cathode material as well as BGPEs are prepared by solution combustion and solution casting technique, respectively. X-ray diffraction (XRD) technique clearly reveals that the cathode material is in pure phase, having well defined layered structure. Thermal, electrical and electrochemical properties of BGPEs are investigated by using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), impedance spectroscopy and linear sweep voltammetry (LSV). It is observed that 70 wt% IL containing BGPE provides maximum Li-ion conductivity (σLi+∼1.1 mS cm−1), thermal (∼250 °C) and electrochemical stability (∼4.3 V vs. Li/Li+). Electrochemical analysis of the cell (Li/70 wt% BGPE/Li1·2Ni0·6Mn0·1Co0·1O2) provides well defined redox peaks corresponding to Ni2+/Ni4+ and it delivers specific discharge capacity of 166 mAh g−1 at 0.1 C-rate and 97% efficiency upto 140 cycle.

6．双性イオン液体のLiイオン電池用電解液としての応用

6．双性イオン液体のLiイオン電池用電解液としての応用

Green Pathway in Utilizing CO2 via Cycloaddition Reaction with Epoxide—A Mini Review

Carbon dioxide (CO2) has been anticipated as an ideal carbon building block for organic synthesis due to the noble properties of CO2, which are abundant renewable carbon feedstock, non-toxic nature, and contributing to a more sustainable use of resources. Several green and proficient routes have been established for chemical CO2 fixation. Among the prominent routes, this review epitomizes the reactions involving cycloaddition of epoxides with CO2 in producing cyclic carbonate. Cyclic carbonate has been widely used as a polar aprotic solvent, as an electrolyte in Li-ion batteries, and as precursors for various forms of chemical synthesis such as polycarbonates and polyurethanes. This review provides an overview in terms of the reaction mechanistic pathway and recent advances in the development of several classes of catalysts, including homogeneous organocatalysts (e.g., organic salt, ionic liquid, deep eutectic solvents), organometallic (e.g., mono-, bi-, and tri-metal salen complexes and non-salen complexes) and heterogeneous supported catalysts, and metal organic framework (MOF). Selection of effective catalysts for various epoxide substrates is very important in determining the cycloaddition operating condition. Under their catalytic systems, all classes of these catalysts, with regard to recent developments, can exhibit CO2 cycloaddition of terminal epoxide substrates at ambient temperatures and low CO2 pressure. Although highly desired conversion can be achieved for internal epoxide substrates, higher temperature and pressure are normally required. This includes fatty acid-derived terminal epoxides for oleochemical carbonate production. The production of fully renewable resources by employment of bio-based epoxy with biorefinery concept and potential enhancement of cycloaddition reactions are pointed out as well.

Lithium ionic conductivity of Li7-3xFexLa3Zr2O12 ceramics by the Pechini method

Li7La3Zr2O12 (LLZO) with garnet structure has been acknowledged as a promising solid electrolyte for the next generation Li-ion batteries owing to its high chemical stability against Li metal and relatively high Li-ion conductivity. In this work, Li7-3xFexLa3Zr2O12 ceramics were prepared by the Pechini method. The influence of Fe substitution on the structure and microstructure of LLZO powder and ceramic were investigated by X-ray diffraction (XRD), TG (DSC)-MS, Raman spectroscopy, scanning electron microscopy (SEM), and impedance spectroscopy. TG-MS and XRD results indicated that LLZO powder could be formed around 750 °C. SEM results showed that the introduction of Fe accelerated densification of LLZO ceramic. The relative density of the composition with x = 0.2 was approximately 95.6%. Its ionic conductivity and activation energy were 4.28 × 10−4 S/cm and 0.27 eV at 30 °C, respectively.

Enhanced ion conduction by enforcing structural disorder in Li-deficient argyrodites Li6−xPS5−xCl1+x

Solid electrolytes with high ionic conductivity and good stability are advantageous over the current liquid electrolytes in rechargeable Li-ion batteries. Argyrodites, Li6PS5X (X ​= ​Cl, Br, or I), with ionic conductivities on the order of mS/cm have attracted tremendous attention. However, the high potential of argyrodites in fast ion conduction is far from being reached. Significant enhancement in ion conduction relies on the fundamental understanding of the contributing factors for fast ion transport. Here, we have systematically prepared highly conductive Li-deficient Li6−xPS5−xCl1+x and examined the influence of Li-deficiency and Cl substitution of S on ion transport using impedance spectroscopy, solid-state NMR, and first-principles calculations. With increased Cl content, the amount of Cl− at S2− (4d) sites increases, forming a dominant 1S3Cl (4d) configuration. In addition, Li+ redistributes with significantly higher mobility. As a result, the activation energy for Li-ion transport decreases, and the conductivity increases to 17 ​mS/cm at 25 ​°C when x equals 0.7 (Li5.3PS4.3Cl1.7). This work not only reports a record ionic conductivity of Cl-containing argyrodites-type fast Li-ion conductors, but also provides new insights into anion disorder-induced ion transport, which has a wide and universal appeal in the development of fast ion conductors and mixed-anion functional materials.

Physical and electrochemical properties of DES solvents based on 2,2,2-trifluorocetamide and LiTFSI salt for Li-ion batteries

The liquid electrolyte transports lithium ions from anode to cathode during charging, and vice versa. The choice of electrolyte is also important since high ionic conductivity between electrodes is essential for high-performance batteries. Liquid electrolytes with lithium salt dissolved in an organic solvent have been widely used since the 1970s when lithium primary batteries were first developed. Most lithium secondary batteries available today use organic electrolytes. Ionic liquids consist of organic cations and inorganic anions, due to the absence of a combustible and flammable organic solvent, they are known to produce safer batteries. Furthermore, they have a high polarity that allows dissolution of inorganic and organic metal compounds, and they can exist in a liquid state over a wide temperature range. Another type of solvent with similar physical properties and phase behavior to ILs is deep eutectic solvents (DESs) about which the first paper was recently published in 2001. These solvents are mixtures that have a much lower melting point than that of any of their individual components, mainly due to the charge delocalization occurring through hydrogen bonds between them. DESs are generally favored over ILs because they are cheaper and easier to prepare with high purity. In this work, Deep Eutectic Solvents (DESs) were prepared by simple mixing Lithium bis[(trifluoromethane)sulfonyl] imide (LiTFSI) salt and 2,2,2-trifluoroacetamide TFA at various ratios ranging from 1:1.5 to 1:4, respectively. The formation of DESs was characterized by Infrared Spectroscopy (IR) and Thermogravimetric analysis (TGA). Their physical and electrochemical properties were also evaluated based on their viscosity, conductivity, and oxidation stability window. Amongst our systems of interest, DES with LiTFSI: FAc ratio of 1:4 is the most promising as the electrolyte for Li-ion batteries, because it exhibited the lowest viscosity (42.2 mPa.s), the highest ionic conductivity (1.53 mS.cm-1 at 30oC) and relatively good anodic stability (5.2 V vs. Li+/Li).

(Invited) Localized High Concentration Electrolytes for Li Metal and Li Ion Batteries

It is well known that a stable and high efficiency Li metal anode (LMA) is critical for rechargeable Li metal batteries (LMBs). Although LMA is kinetically unstable with non-aqueous electrolyte, Localized High Concentration Electrolytes (LHCEs) can largely minimize the side reaction between LMA and electrolyte, therefore enable a dynamically stable LMA for long term cycling of li metal batteries. In this work, we report a series of LHCEs we developed recently that are highly stable with both LMA and high voltage cathode such as Ni rich LiNixCoyMn1-x-yO2 (x ≥ 0.6), LiCoO2 etc. These LHCEs not only exhibit the advantage of high concentration electrolyte, but also exhibit low viscosity, low cost of the low concentration electrolytes. Furthermore, these electrolytes can be tailored to be non-flammable and stable at low temperature. With appropriate additives, these LHCEs can also largely improve the stability of Si based Li ion batteries. The excellent performance of these batteries are mainly due to the formation of inorganic rich (such as LiF and Li2O) solid electrolyte interphase (SEI) on LMA and cathode electrolyte interphase (CEI) in these electrolytes. The monolithic solid electrolyte interphase (SEI) generated in some of these electrolytes is largely different with those of mosaic- or multilayer-type SEIs reported before. These electrolytes not only can improve the stability of LMA, but also greatly suppresses the phase transformation (from layer structure to rock salt) of the cathode and prevent dissolution of transition metal element in bulk cathode. Therefore, excellent cell performances in terms of long-term cycling stability and high rate capability is realized in high voltage LMBs together with reduced safety concerns. The fundamental mechanism behind the stability of these electrolytes to both LMA and high voltage cathode will also be discussed.

Safe Electrolytes for Li-Ion Batteries

Li-ion batteries are the critical enabling technology for the portable devices, electric vehicles (EV), and renewable energy. However, the safety and energy density of current Li-ion batteries still need to be improved to satisfy the requirements for these applications. We systematically investigated the electrochemical performance of the nonflammable fluoridated organic electrolytes, water-in-salt electrolytes and solid state electrolytes for high energy Li and Li-ion batteries. The critical issues of these safe electrolytes are also discussed

Synthesis and Analysis of Ionic Liquid As Additive for Li-Ion Battery Electrolyte

Lithium ion batteries are promising power sources for various applications such as portable electronics and electrical vehicles, due to their high specific energy density and long cycle life. As one key component of lithium ion battery, the electrolyte should allow lithium ion transport but prevent electron conduction. One big challenge of lithium ion battery is that the high voltage and high current in the charge process can cause self-decomposition of the electrolyte, leading to combustion of the battery. In order to solve the combustion problem in the fast charge process, new electrolyte materials with high ionic conductivity and good chemical stability are urgently needed.Ionic liquid is usually organic salt consisting of anion and cation with low vapor pressure, high boiling point, high ionic conductivity, large specific heat capacity, and non-flammable characteristics. Ionic liquid is aqueous at or near the room temperature. The features of ionic liquid such as the high heat resistance and wide liquid temperature range make it a promising electrolyte material for lithium ion battery.This project aims at tailoring the suitable structure of ionic liquid as the additive for lithium ion battery. Our ionic liquid is a designed composition of anion of TFSI as SEI forming additive and imidazole based cation. A two-step process has been developed for synthesizing ionic liquid. The physical and chemical properties of the ionic liquid were measured to evaluate the feasibility of applying ionic liquid to lithium ion battery.Both the density and the viscosity of the ionic liquid are measured at different temperatures. The density was found to decrease linearly with temperature in both single and binary system. The determined negative excess molar volume of ethyl acetate and ionic liquid system is relative to the interaction between different molecules. The viscosity of the analyzed electrolyte solvent was found to decrease linearly with increasing temperature. Arrhenius-like law was found to be able to fit the measured data well. The fitting parameters were able to predict viscosity at different temperature.The conductivity of the whole electrolyte system and compatibility with the active materials will be tested and discussed in the next study.