Electrolytes For Li-ion Batteries Research Articles

NiII and CuII coordination polymers as anode materials and their compatibility with different electrolytes in Li-ion batteries

The effect of various types of electrolytes on the operation of coordination polymers based on NiII or CuII in lithium-ion batteries has been examined. Cyclic voltammetry, galvanostatic cycling and quantum chemical modeling have been used to study the processes of lithiation and delithiation. It was shown that the use of a new electrolyte based on a mixture of 1 M LiN(CF3SO2)2 in 1,3-dioxolane–1,2-dimethoxyethane and 1 M LiPF6 in ethylene carbonate–dimethyl carbonate improved battery performance, while cycling in the range of 0.2–2.5 V increased the discharge capacity up to 177–188 mA h g−1 and stabilized the charge–discharge processes.

Revisiting Ultrafast Dynamics in Carbonate-Based Electrolytes for Li-Ion Batteries: Clarifying 2D-IR Cross-Peak Interpretation.

Understanding chemical exchange in carbonate-based electrolytes employed in Li-ion batteries (LIBs) is crucial for elucidating ion transport mechanisms. Ultrafast two-dimensional (2D) IR spectroscopy has been widely used to investigate the solvation structure and dynamics of Li-ions in organic carbonate-based electrolytes. However, the interpretation of cross-peaks observed in picosecond carbonyl stretch 2D-IR spectra has remained contentious. These cross-peaks could arise from various phenomena, including vibrational couplings between neighboring carbonyl groups in the first solvation shell around Li-ions, vibrational excitation transfers between carbonyl groups in distinct solvation environments, and local heating effects. Therefore, it is imperative to resolve the interpretation of 2D-IR cross-peaks to avoid misinterpretations regarding ultrafast dynamics found in LIB carbonate-based electrolytes. In this study, we have taken a comprehensive investigation of carbonate-based electrolytes utilizing 2D-IR spectroscopy and molecular dynamics (MD) simulations. Through meticulous analyses and interpretations, we have identified that the cross-peaks observed in the picosecond 2D-IR spectra of LIB electrolytes predominantly arise from intermolecular vibrational excitation transfer processes between the carbonyl groups of Li-bound and free carbonate molecules. We further discuss the limitations of employing a picosecond 2D-IR spectroscopic technique to study chemical exchange and intermolecular vibrational excitation transfer processes, particularly when the effects of the molecular photothermal process cannot be ignored. Our findings shed light on the dynamics of LIB electrolytes and resolve the controversy related to 2D-IR cross-peaks. By discerning the origin of these features, we could provide valuable insights for the design and optimization of next-generation Li-ion batteries.

Feasibility of Multifunctional Cellulose-Based Polysalt as a Polymer Matrix for Li Metal Polymer Batteries.

Li metal secondary batteries known for their high energy and power density are the much-awaited energy storage systems owing to the high specific capacity of Li metal. However, due to the instability of Li metal with common Li-ion battery electrolytes, a combination with a polymer electrolyte seems to be an effective strategy to alleviate the safety issues of employing Li metal and provide design conformity to the system. Current trends show improvements in different aspects, such as improving ionic conductivity, single-ion conductivity, mechanical stability, and electrochemical stability. A combination of all these properties has been a bottleneck for the development of polymer electrolytes for safe and efficient operation of all solid-state batteries. Herein, a multifunctional polysalt has been synthesized from green and sustainable materials, namely, ethyl cellulose, plasticized with adiponitrile, that contributes to meeting the critical properties enabling high compatibility with Li metal and a quasi-single-ion-conducting property while simultaneously acting as a matrix/filler for efficient operation of the cells. This multifunctional polymer matrix inhibits further decomposition of nitrile-based plasticizers on Li metal anodes with the formation of a favorable Li metal anode interface, thus enabling the utilization of high-voltage stable nitrile-based plasticizers (4.2 V) to be implemented as an electrolyte component for realization of high-voltage Li metal anode polymer batteries.

An easily degradable composite separator with high affinity to ionic-liquid-based electrolytes for safe Li-ion batteries

Ionic-liquid-based electrolytes emerge as a viable alternative to commercial carbonate electrolytes due to their superior stability and safety, especially at high temperatures. However, their affinity to the currently widely used polyolefin-based separators is poor. Herein, an economical and environmentally friendly separator composed of hydroxyapatite and cellulose nanofibers is designed and fabricated. The composite separator possesses a fibrous network with a large surface area and rich polar groups, featuring high wettability and ionic conductivity based on carbonate and ionic-liquid-based electrolytes. The LiFePO4/Li half-cell with this separator exhibits superior cyclability with a high capacity of ∼130 mAh g−1 using an ionic-liquid electrolyte at room temperature. Moreover, the resulting composite separator is thermally stable, and the assembled batteries achieve outstanding cyclability at 80 °C. Furthermore, the universality of the separator is demonstrated by successful employment in sodium and zinc-ion batteries. The as-fabricated composite separator is easily degradable and promising as an environmental-benign substitute to conventional polyolefin-based separators for next-generation batteries.

Smectic solid electrolytes containing lamellar conducting channels for solvent-free lithium-ion batteries with a thermal switch on/off performance

Developing electrolytes with desirable electrochemical performance and robust stability remains a huge challenge to meet the efficiency and durability demands of energy storage and conversion devices. Herein, the potential of ionic liquid crystals as high-performance electrolytes is demonstrated. Smectic ionic liquid crystals only consisting of conventional [C14Mim][BF4] and LiBF4 are designed and prepared as electrolytes for solvent-free lithium-ion batteries. [C14Mim][BF4] has good miscibility with LiBF4 to form smectic liquid crystals. LiBF4 is highly concentrated by [C14Mim][BF4] layers in the smectic electrolytes to form dynamic lamellar conducting channels, which enable considerable ion conductivities of 10–4 ∼ 10–3 S cm−1. The smectic electrolytes possess robust cyclic stability and energy conversion efficiency in Li/LiFePO4 batteries, which show a charge/discharge capacity of 154.7 mA h g−1 at a 1 C current density, as well as stable performance after 100 charge/discharge cycles even at 80 ℃. Additionally, the phase transition behavior of the electrolytes can be applied as a smart switch to thermally tune on/off the batteries. The electrolytes show almost no charge/discharge behavior under crystal phase, but automatically operate efficiently with charge/discharge capacities >150 mA h g−1 once entering the smectic phase. The present work sheds new light on developing high-performance and smart electrolytes for solvent-free Li-ion batteries.

Investigating the amount of water on reducing Lix(OH)yClz hydroxide phases in the synthesis of Li3OCl anti-perovskite as a solid electrolyte in Li-ion batteries

ABSTRACT The Li3OCl solid electrolyte was synthesized in the present study via the hydrothermal method. In order to investigate the effect of water on the stability of the Li3OCl phase and reduce the amount of secondary hydroxide phases, different molar ratios of water were added to the precursors during the synthesis procedures. Employing XRD, DSC, FE-SEM, EIS, and CV techniques revealed that the LiCl: LiOH: H2O (1:2:10) molar ratio has better phase stability and fewer undesired hydroxide phases. The DSC results also showed that during the first heat treatment cycle, the Lix(OH)yClz phases were converted to the Li3OCl phase. After heat treatment, the final structure was characterized as a glass-ceramic structure. At 60°C and 110°C, respectively, the synthesized Li3OCl reached an ionic conductivity of 5.0 × 10−2 mS cm−1 and 0.76 mS cm−1. Also, the activation energy of 0.27 eV in the 60–110°C temperature range was recorded for the synthesized Li3OCl. The chemical stability of the synthesized Li3OCl was confirmed during lithiation/delithiation from −1.5 to 4 V at 130°C.

Revisiting the stability of aluminum current collectors in carbonate electrolytes for High-Voltage Li-ion batteries

Anodic dissolution (often referred to as corrosion) of the aluminum positive electrode current collector above 3 V vs. Li+/Li can become performance-limiting in high-voltage Li-ion batteries. Herein, the results of a systematic reevaluation of this phenomenon at potentials up to 5.0 V vs. Li+/Li, using different carbonate electrolytes containing LiPF6, LiFSI or LiTFSI, are presented. The anodic dissolution is most likely caused by etching of the Al2O3 passive layer by protons released during the oxidation of the solvent. This sparks off a second oxidation step, involving the oxidation of the aluminum. While a passive AlF3 layer is formed in 1.0 M LiPF6, extensive anodic dissolution of aluminum is seen in 1.0 M LiFSI or LiTFSI at potentials where the solvent undergoes oxidation. In 5.0 M LiFSI, a passive layer of AlF3 is, however, formed most likely due to the presence of fluoride as an impurity in the LiFSI. No significant improvement was seen when using carbon-coated aluminum electrodes.

A full metal-free battery operating under cold condition enabled by an antisolvent

Metal-free batteries provide a more sustainable and environmental-friendly alternative to current popular batteries using nonrenewable metals. Alcohols as anti-solvents have been used in the electrolytes in Li-ion batteries (LIBs) and zinc-ion batteries (ZIBs), as they bring new properties with regards to the solvation sheath and water activity to the electrolytes. In this work, we explore the application of methanol (CH3OH) as an antisolvent in the electrolyte in a metal-free ammonium-ion battery (AIB) for operation at low temperature, with polyaniline (PANI) as anode and polypyrrole (PPy) as cathode. The addition of CH3OH alters the solvation sheath of the NH4+ and reduces the activity of H2O by forming hydrogen bonds in the solution, thereby decreasing the freezing point of the electrolyte. Through this strategy, a lower freezing point of the electrolyte is realized without using ultrahigh concentration of salts in aqueous solution. The resulted full metal-free battery using a 4 m ammonium acetate electrolyte is able to operate at -20°C, while long cycling at subzero temperatures has never been reported for ammonium-ion batteries before. Further, the CH3OH-H2O volume ratio can be optimized to 65-35, leading to an ammonium-ion battery that exhibits a capacity of 73.23, 48.32 and 32.88 mAh/g, as well as a capacity retention of 87.79%, 90.12% and 74.33% after 100 cycles at 0.1 A/g, at 25°C, 0°C and -20°C, respectively. In this work, an antisolvent is used in non-metal ammonium-ion batteries for the first time, engendering the battery anti-freezing properties. As such, this study opens the door to the realization of novel metal-free batteries with lower cost and better performance for applications in frigid environments.

Adoption of Dimethoxyethane and 1,3-Dioxolane in Electrolyte for Fast Charging of Li-Ion Battery

In this work, dimethoxyethane (DME) and 1,3-dioxolane (DOL) are studied as the co-solvent of an advanced electrolyte for fast charging of Li-ion batteries by using lithium bis(fluorosulfonyl)imide (LiFSI) as a salt and fluorinated ethylene carbonate (FEC) as an additive. It is shown that even when used with LiFSI and FEC, neither DME nor DOL constitute a suitable electrolyte for Li-ion batteries, either because of their inability to form a robust solid-electrolyte interphase (SEI) with graphite (Gr) anodes or because of their oxidative instability against oxygen released from the delithiated LiNi0.80Co0.10Mn0.10O2 (NCM811) and LiNi0.80Co0.15Al0.05O2 (NCA), respectively. However, using 30% FEC as the co-solvent can make 1:1 DME/DOL mixture compatible with high-voltage Li-ion batteries and combining it with conventional ethylene carbonate (EC) and ethyl methyl carbonate (EMC) significantly enhances the fast charging capability of Li-ion batteries. As a result, an advanced electrolyte composed of 1.2 m (molality) LiFSI 1:1:1:2 DME/DOL/EC/EMC + 10% FEC (all by wt.) offers much improved fast-charging performances in terms of capacity and capacity retention for a 200 mAh Gr/NCA pouch cell, compared with a 1.2 m LiFSI 3:7 EC/EMC baseline electrolyte. AC impedance analysis reveals that the significant improvement is attributed to a much reduced charge transfer resistance, while the advanced electrolyte has little effect on the bulk and SEI resistances.

Role of Solvent Isomerism in Mixed Carbonate Electrolytes for Li-Ion Batteries

Role of Solvent Isomerism in Mixed Carbonate Electrolytes for Li-Ion Batteries

Eutectic Electrolytes Composed of Li Salt and Sulfones

Sulfone-based highly concentrated electrolytes are promising electrolytes for high-voltage Li-ion batteries (LIBs), owing to the high thermal and oxidative stabilities of sulfones. In addition, highly concentrated Li salt/sulfone electrolytes exhibit unique Li+ ion hopping/exchange conduction mechanism and high Li+ ion transference number (>0.6).1,2 However, the application of these electrolytes at low temperatures is limited due to the precipitation of a stable crystalline solvate. In this study, the applicability of ternary mixtures of Li salt, sulfolane (SL), and dimethyl sulfone (DMS) as LIB electrolytes was assessed. Due to the increased entropy of mixing, the crystallization of the solvates was suppressed in the ternary electrolytes, resulting in a wide temperature range of liquid sate of the electrolytes.3 In the ternary electrolytes, the network structures of Li+–sulfone–Li+ and Li+–anion–Li+ were formed, and Li+ ion dynamically exchanges sulfones and anions and diffuses more rapidly than these ligands, resulting in a relatively high Li+ transference number. Highly reversible charge–discharge behaviors of the LiCoO2 and graphite electrodes were attained using the ternary electrolyte. Despite the lower ionic conductivity of the sulfone-based electrolyte, the rate capability of the Li/LiCoO2 cell with the ternary electrolyte was comparable to that in a conventional carbonate-based electrolytes. Acknowledgements This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813 and JP22H00340). References K. Dokko et. al., J. Phys. Chem. B 2018, 122, 10736.Y. Ugata et. al., J. Phys. Chem. B 2021, 125, 6600.Y. Ugata et. al., J. Phys. Chem. C 2022, 126, 10024.

(Invited) Modeling the Charge Transfer Reactions at Li/SEI/Electrolyte Interfaces in Lithium-Ion Batteries

Two kinds of charge transfer reactions are critical for the performance and life of lithium battery: the desired ion transfer reaction occurring during each charge/discharge cycle, , and the undesired electron transfer reactions leading to the parasitic chemical decomposition of the electrolyte and solid electrolyte interphase (SEI) formation/growth. The heterogeneous multi-component nature of SEI dominates its ionic and electronic transport properties and controls these two charge transfer reactions. Density Functional Theory (DFT)-informed multiscale modeling has been providing valuable insights under the scarcity of quantitative experiments. For example, the LiF/Li2CO3 interface was demonstrated to increase the ionic conductivity of mixed SEI nanocomposite by forming an ionic space charge region near the interface and promoting more Li-ion interstitials in Li2CO3, although LiF itself has low Li-ion conducting carriers and conductivity. To form a LiF-rich SEI layer, the electrolyte compositions need to be designed. Since the SEI formation occurs on the charged surface, the electric double layer (EDL) structure near the charged surfaces needs to be incorporated into the modeling. Here interactive classical molecular dynamics (MD), DFT, and data statistical analysis were combined to illustrate the effect of EDL on SEI formation in two essential electrolytes, the carbonate-based electrolyte for Li-ion batteries and the ether-based electrolyte for batteries with Li-metal anodes. It was found the effectiveness of adding fluoroethylene carbonate (FEC) to form the beneficial F-containing SEI component (e.g., LiF) varies with the electrolyte and temperature, because of the interplay of ion-solvent interactions with the surface charge. These integrated modeling provided quantitative guidance for electrolyte/SEI/Li-metal interface design.

A Recyclable Solid Electrolyte for Li-Ion Batteries Composed of Supramolecular Nanostructures

The recyclability of Li-ion batteries is a critical goal but is technically challenging and often impractical due to the complex structure of mixed materials and the irreversible process of production. We investigated the use of organic small molecule self-assembled nanoribbons as an electrolyte material because they offer precise spatial arrangement, high surface areas, tunable surface chemistry, and most notably here, reversible structural formation. In this study, we synthesized nanoribbons by self-assembly of aramid-containing amphiphiles that overcome structural stability problems, and we systematically modified the surface chemistry to promote Li-ion conductivity. We investigated the performance and transport mechanism of these supramolecular nanomaterials as a solid electrolyte for Li-ion batteries. Furthermore, we show direct recyclability of the end-of-life cell. Figure 1

In-Operando Isothermal Microcalorimetry to Accelerate Screening of New Battery Chemistries

Screening new cell chemistries using traditional electrochemical methods is a time prohibitive process that significantly slows the pace of research. These methods involve cycling the cell until signs of degradation or sufficient capacity fade are evident, and typically take months to complete. In-operando isothermal microcalorimetry is an established but underutilized technique for measuring the activity of parasitic, or non-reversible reactions during charge cycling [1,2,3,4]. A parasitic reaction is a blanket term for any side reactions that occur within a battery, including solvent breakdown, lithium plating, self-discharge reactions, and growth or decomposition of the solid electrolyte interphase. Battery formulations with high parasitic heat are strongly correlated with early cell failure. Compared to electrochemical cycling, the average parasitic heat over the full voltage range can be determined in a time frame as low as 2 weeks, allowing researchers to realize a time savings up to 75%. Additional time savings are also possible if only a narrow voltage range is of interest.In this study, we present results that demonstrate the measurement of the parasitic heat of a commercial 18650 lithium-ion battery using the TA Instruments Battery Cycler Microcalorimeter Solution. This method involves slow galvanostatic cycling at isothermal conditions with a simultaneous measurement of heat flow, voltage, and applied current. The parasitic heat is isolated from the total heat flow using the Integration-Subtraction method, with calculations performed automatically by the software [1]. The coulombic efficiency is also measured per cycle, showing an inverse relationship to the parasitic power. As a screening tool, this data could be used to select battery formulations most likely to meet performance goals in long-term cycling experiments, rather than wasting valuable time and lab space on a trial-and-error approach. The results highlight how in-operando isothermal microcalorimetry is a powerful screening tool for investigating the efficiency of new cell chemistries and electrolyte formulations in a fraction of the time compared to traditional methods.[1] L.J. Krause, L.D. Jensen, V.L. Chevrier. Measurement of Li-Ion Battery Electrolyte Stability by Electrochemical Calorimetry. J. Electrochem. Soc. 2017, 164 (4), A889-A896.[2] L.J. Krause, L.D. Jensen, J.R. Dahn. Measurement of Parasitic Reactions in Li Ion Cells by Electrochemical Calorimetry. J. Electrochem. Soc. 2012, 159 (7), A937-A943.[3] J.C. Burns, Adil Kassam, N.N. Sinha, L.E. Downie, Lucie Solnickova, B.M. Way, J.R. Dahn. Predicting and Extending the Lifetime of Li-Ion Batteries. J. Electrochem. Soc. 2013, 160, A1451.[4] E. R. Logan, A. J. Louli, Matthew Genovese, Simon Trussler,and J. R. Dahn. Investigating Parasitic Reactions in Anode-Free Li Metal Cells with Isothermal Microcalorimetry. J. Electrochem. Soc. 2021, 168, 060527.

Aging-driven composition and distribution changes of electrolyte and graphite anode in 18650-type Li-ion batteries

Aging-driven composition and distribution changes of electrolyte and graphite anode in 18650-type Li-ion batteries

Machine learning force fields for molecular liquids: Ethylene Carbonate/Ethyl Methyl Carbonate binary solvent

Highly accurate ab initio molecular dynamics (MD) methods are the gold standard for studying molecular mechanisms in the condensed phase, however, they are too expensive to capture many key properties that converge slowly with respect to simulation length and time scales. Machine learning (ML) approaches which reach the accuracy of ab initio simulation, and which are, at the same time, sufficiently affordable hold the key to bridging this gap. In this work we present a robust ML potential for the EC:EMC binary solvent, a key component of liquid electrolytes in rechargeable Li-ion batteries. We identify the necessary ingredients needed to successfully model this liquid mixture of organic molecules. In particular, we address the challenge posed by the separation of scale between intra- and inter-molecular interactions, which is a general issue in all condensed phase molecular systems.

Enhanced Li+ conductivity of Li7La3Zr2O12 by increasing lattice entropy and atomic redistribution via Spark Plasma Sintering

Cubic Li7La3Zr2O12 (c-LLZO) is an ideal solid-state electrolyte for Li-ion batteries. The Li diffusivity at 24d site is a rate-determining step of the ionic conductivity. Aluminium is commonly used to synthesise c-LLZO. However, Al3+ prefers to occupy the 24d over 96h. To improve the ionic conductivity of Al-doped LLZO, minimizing the occupation of Al at 24d is shown to be crucial. In this work, SPS (Spark Plasma Sintering) is employed primarily due to its capability of metastable phase stabilization via a non-equilibrium process and ion redistribution related electromigration process. X-ray powder diffraction refinement reveals that occupancy of Al at 24d site decreased and lattice distortion index increase of SPS processed Al-doped c-LLZO. The lattice distortion index is closely tied to lattice entropy, i.e., configuration and vibrational entropy. Increasing lattice entropy can reduce the energy barriers between Al and Li’s 24d and 96h sites, stabilising Al3+ occupancy at 96h site. After SPS parameter optimisation, the high ionic conductivity of 2.6 × 10–4 S·cm-1 and low electronic conductivity of 10–7 S·cm-1. This study offers a new perspective on using SPS to modify the lattice structure, with potential benefits beyond simply densifying the samples. Highlighting the importance of high lattice entropy is favourable in enhancing ionic conductivity.

Spectroscopic neutron imaging for resolving hydrogen dynamics changes in battery electrolytes

We present the use of spectroscopic neutron imaging (SNI), a bridge between imaging and scattering techniques, for analyzing battery electrolytes. The scattering information of CHn–based organic solvents and electrolytes was mapped in a two-dimensional space through time-of-flight neutron imaging, which exploits the wavelength-dependent properties of hydrogen atoms. The results show partial solidification and concertation change of electrolyte as a function of temperature. Our investigation demonstrates a novel approach to tracking real-time physical and chemical changes in H-containing compounds, by which limitations of new electrolyte mixtures and additives can be evaluated. The sensitivity of SNI to hydrogen in CHn functional groups extends the use of spectral methods to inspect electrolytes in Li-ion batteries and organic solvents for relevant applications beyond electrochemical systems.

Matching silicon-based anodes with sulfide-based solid-state electrolytes for Li-ion batteries

Thanks to their high ionic conductivity and appropriate mechanical properties, sulfide-based solid electrolytes (SSE) are increasingly studied for a use in all-solid-state batteries (ASSBs). Silicon is abundant, non toxic and has a high theoretical capacity, and therefore is a promising active material in ASSBs. We first study the compatibility between two different solid electrolytes with similar ionic conductivity, Li10SnP2S12 (LSnPS) and Li6PS5Cl (LPSCl), and micron-sized silicon based anode. LPSCl appears to be less reactive than LSnPS and it is then used to determine the most appropriate silicon size and shape for efficient cycling. Two silicon materials are compared, micron-sized silicon particles (μSi) and silicon nanowires (SiNWs). Energy Dispersive X-ray spectroscopy (EDX) mapping of the composite powders shows a better dispersion of the SiNWs in the LPSCl matrix. Galvanostatic cycling and Electrochemical Impedance Spectroscopy (EIS) measurements highlight the greater compatibility of SiNWs compared to μSi in ASSBs with a high specific delithiation capacity of 2600 mAh/gSi at the first cycle, while limiting the polarization and maintaining a relatively stable lithiation mechanism during cycling.

Enhancing ionic conductivity of garnet-type Nb-doped Li7La3Zr2O12 by cerium doping

We investigated the effect of additional doping with Ce on the ionic conductivity of the Nb-doped Li7La3Zr2O12 (LLZO) garnet ceramics using a combination of experimental and modeling approaches. Our results indicate that Ce doping can alter lattice parameters of the LLZNO, leading to the enhanced lithium ionic conductivity. The Ce, Nbco-doped LLZO (LLZNCO) structure with composition Li6.5La3Zr1.5‒xNb0.5CexO12 (x = 0.125) exhibits a lower activation energy (Ea = 0.39 eV) than Li6.5La3Zr1.5Nb0.5O12 (LLZNO) (Ea = 0.41 eV). Furthermore, Ce doping leads to an increase in Li+ conductivity from 6.4 × 10−4 to 7 × 10−4 S/cm at room temperature. In addition, we discuss the diffusivity and conductivity of our samples using ab initio molecular dynamics simulations and propose possible mechanisms to explain the enhanced Li-ion conductivity caused by co-doping with Ce and Nb. Our results demonstrate that the LLZNCO ceramics are promising candidates for potential solid-state electrolytes for Li-ion batteries.