Li-ion Electrolyte Research Articles

Modeling High Concentration Bisalt-in-Sulfolane Electrolytes and the Observation of Ligand-Bridged Cation-Pair Complexes.

Despite the abundance of sodium over lithium in Earth's crust and the copious amounts of expensive lithium salt required to make Li-ion high-concentration electrolytes (HCEs), studies of HCEs made from sodium salts remain sparse. A comparative molecular-level study of Li- and Na-ion HCEs and mixed cation or bisalt HCEs in an organic solvent is missing. To fill this gap, we studied model HCEs of pure and mixed Li and Na salts of bis(fluorosulfonyl)amide (FSI) in sulfolane using a confluence of classical molecular dynamics (MD), ab initio MD (AIMD) simulations, and quantum chemical cluster calculations. While Li-ion HCEs display transport properties superior to those of Na-ion HCEs, the latter's performance can be considerably improved by replacing even 25% of Na-ions with Li-ions. While the effects of doping are largely systemic, a larger sensitivity of the identity of solvation shells of Li-ions to the Li-content of the HCE is observed; in contrast, those of Na-ions are more oblivious to it. Fascinating ligand-bridged, short-distance cation pairs observed in the classical MD simulations are confirmed using density functional theory-based AIMD simulations. Quantum chemical calculations in the gas phase reveal the thermodynamic stability of such cation pairs complexed with multiple anions and solvent molecules.

Lift-Out Specimen Preparation and Multiscale Correlative Investigation of Li-Ion Battery Electrodes Using Focused Ion Beam-Secondary Ion Mass Spectrometry Platforms.

Advanced characterization is paramount to understanding battery cycling and degradation in greater detail. Herein, we present a novel methodology of battery electrode analysis, employing focused ion beam (FIB) secondary-ion mass spectrometry platforms coupled with a specific lift-out specimen preparation, allowing us to optimize analysis and prevent air contamination. Correlative microscopy, combining electron microscopy and chemical imaging of a liquid electrolyte Li-ion battery electrode, is performed over the entire electrode thickness down to subparticle domains. We observed a distinctive remnant lithiation among interparticles of the anode at the discharge state. Furthermore, chemical mapping reveals the nanometric architecture of advanced composite active materials with a lateral resolution of 16 nm and the presence of a solid electrolyte interface on the particle boundaries. We highlight the methodological advantages of studying interfaces and the ability to conduct high-performance chemical and morphological correlative analyses of battery materials and comment on their potential use in other fields.

Predicting Reactivity and Passivation of Solid-State Battery Interfaces.

In this work, we build a computationally inexpensive, data-driven model that utilizes atomistic structure information to predict the reactivity of interfaces between any candidate solid-state electrolyte material and a Li metal anode. This model is trained on data from ab initio molecular dynamics (AIMD) simulations of the time evolution of the solid electrolyte-Li metal interfaces for 67 different materials. Predicting the reactivity of solid-state interfaces with ab initio techniques remains an elusive challenge in materials discovery and informatics, and previous work on predicting interfacial compatibility of solid-state Li-ion electrolytes and Li metal anodes has focused mainly on thermodynamic convex hull calculations. Our framework involves training machine learning models on AIMD data, thereby capturing information on both kinetics and thermodynamics, and then leveraging these models to predict the reactivity of thousands of new candidates in the span of seconds, avoiding the need for additional weeks-long AIMD simulations. We identify over 300 new chemically stable and over 780 passivating solid electrolytes that are predicted to be thermodynamically unfavored. Our results indicate many potential solid-state electrolyte candidates have been incorrectly labeled unstable via purely thermodynamic approaches using density functional theory (DFT) energetics, and that the pool of promising, Li-stable solid-state electrolyte materials may be much larger than previously thought from screening efforts. To showcase the value of our approach, we highlight two borate materials that were identified by our model and confirmed by further AIMD calculations to likely be highly conductive and chemically stable with Li: LiB13C2 and LiB12PC.

Supramolecular Assembly of Fused Macrocycle-Cage Molecules for Fast Lithium-Ion Transport.

We report a new supramolecular porous crystal assembled from fused macrocycle-cage molecules. The molecule comprises a prismatic cage with three macrocycles radially attached. The molecules form a nanoporous crystal with one-dimensional (1D) nanochannels. The supramolecular porous crystal can take up lithium-ion electrolytes and achieve an ionic conductivity of up to 8.3 × 10-4 S/cm. Structural analysis and density functional theory calculations reveal that efficient Li-ion electrolyte uptake, the presence of 1D nanochannels, and weak interactions between lithium ions and the crystal enable fast lithium-ion transport. Our findings demonstrate the potential of fused macrocycle-cage molecules as a new design motif for ion-conducting molecular crystals.

Improved Wide Temperature and Rate Performance in Li-Ion Batteries with Fluorinated Electrolyte Solvents

Commercial electrolytes include organic solvents unable to withstand the conditions required for the rapidly growing Li-ion battery industry, such as extreme temperatures and charge rates. The thermal and electrochemical stability limits of these solvents restrict the development of Li-ion batteries needed to sustain automotive electrification and other industrial applications. Further efforts are needed to enable electrolyte formulations suited for the operational demands in the market.Koura has designed a series of fluorinated materials for use in Li-ion electrolytes that demonstrate improved performance and safety over conventional commercial electrolytes. The impact of Koura’s fluorinated solvents on performance in 4.3V Gr/NMC811 was examined, with a particular focus on benefits seen on extreme temperature and rate performance. Testing included cycling and rate performance across a range of temperatures from -20 °C to 45 °C and cycling conditions from C/2 to 4C. It has been found that these materials improve low temperature performance and reduce gassing and increase capacity retention during high-temperature and fast charge cycling. Where appropriate, performance of Koura materials is compared to common commercial solvents.To elucidate the mechanisms responsible for the observed improvements, comprehensive post-test analysis has been conducted, including gas composition analysis and quantification via gas chromatography, bulk electrolyte composition analysis via NMR spectroscopy, and surface layer characterization via XPS and SEM. Bulk transport properties of the materials and electrolytes, including conductivity, viscosity, and Li+ solvation, are correlated to performance benefits.This presentation will show Koura’s efforts to fill a major gap in the demands of the Li-ion battery industry today through the design of fluorinated materials and optimization of advanced electrolyte formulations. Specifically, we will present data highlighting the performance of fluorinated compounds on improving battery performance under strenuous conditions with respect to both temperature and cycling rate. Results from fundamental mechanistic studies will be discussed to highlight the mechanisms underlying the observed performance improvements.

Stable Lithium Metal Batteries Enabled by Dilute Cationic Additives

Conventional Li-ion electrolytes consist of carbonate solvents and Li-ion salts that were made for carbonaceous negative electrodes. When the electrolytes are used with metallic lithium anodes, carbonate electrolytes lead to low charge-discharge cycle stability due to adverse reactive species at the anode surface.1-4 This reactive species are called the solid electrolyte interface (SEI).1 SEI instabilities/inhomogeneities result in its continuous thickening and formation of electronically non-active dead lithium.2 SEI composition and structure are affected by both solvent and electrolyte chemistry in bulk solution and, more importantly, at the electrode-electrolyte interface.4 Current research studies suggest that X-rich (where X is a halogen) SEI yields superior performance compared to halogen-free SEI.1,5 Electrolytes that have large volume fractions of halogenated species have statistically higher probability to be reduced at the electrode surface and yield X-rich SEI layers.6 Therefore, the use of halogenated solvent and/or high concentrated (> 1 M) lithium salt with halogenated anions has been actively explored for LiMBs. However, the high cost of Li salts and high viscosity of the electrolyte at high salt concentration make the concentrated electrolytes unrealistic for commercial battery applications. In search of a cost-effective solution for high performance LiMBs, halogenated electrolyte additives could serve as an ideal approach since only a small amount of the additive would be potentially required to induce similar X-rich interface that can be seen in the case of the halogenated ether electrolyte. In this meeting abstract, we present a new concept that leverages favorable electrostatic interactions with the electrolyte additive to drive the formation of robust SEI layers even at low additive content. Specifically, custom-designed additives can be electrostatically attracted to the negatively charged electrode, creating a high population of halogenated species at the anode surface even at a dilute Li salt concentration. Effective SEI formation with a low-concentration additive circumvents the challenges associated with the current state-of-the-art approach of using halogenated species at high concentration (i.e., unfavorably high solution viscosity and high cost). Reference 1 Louli, A. J. et al. Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis. Nature Energy 5, 693-702, (2020).2 Chen, K.-H. et al. Dead lithium: mass transport effects on voltage, capacity, and failure of lithium metal anodes. Journal of Materials Chemistry A 5, 11671-11681, (2017).3 Lin, D. et al. Three-dimensional stable lithium metal anode with nanoscale lithium islands embedded in ionically conductive solid matrix. Proc Natl Acad Sci U S A 114, 4613-4618, (2017).4 Lin, D., Liu, Y. & Cui, Y. Reviving the lithium metal anode for high-energy batteries. Nat Nanotechnol 12, 194-206, (2017).5 Yu, Z. et al. Molecular design for electrolyte solvents enabling energy-dense and long-cycling lithium metal batteries. Nature Energy 5, 526-533, (2020).6 Yamada, Y., Wang, J., Ko, S., Watanabe, E. & Yamada, A. Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy 4, 269-280, (2019).

Enhancing Shelf-Life of Electrolytes with LiPF6 By Increasing Stability Under Commercially Relevant Storage Conditions

Lithium hexafluorophosphate (LiPF6) salt is the most commonly used lithium salt in commercial Li-ion batteries due to its high conductivity, passivation of Al current collectors for positive electrodes, and participation in SEI layer formation at graphite anodes.1 However, LiPF6 suffers from poor thermal stability and poor stability toward protic species (like water) leading to decomposition that can significantly reduce Li-ion battery performance especially under the extreme conditions demanded by today’s industrial applications. Specifically, LiPF6 decomposition leads to HF generation, especially in the presence of water2, which results in multiple negative outcomes in Li-ion cells including dissolution of cathode materials and gas generation.3 Conditions during electrolyte blending, transport, and/or storage often exacerbate LiPF6 instability and increase HF generation.To date, efforts to replace LiPF6 have not proven to be commercially successful, therefore strategies to improve the stability of LiPF6 electrolytes under relevant storage conditions are critical to support the deployment of Li-ion batteries. Koura has extensively characterized the degradation of LiPF6 as a function of multiple conditions, including temperature, water content, and electrolyte composition to inform the design of strategies to improve stability.This presentation will summarize Koura’s efforts to understand LiPF6 decomposition under conditions relevant to the Li-ion electrolyte supply chain. Specifically, we will present data showing a series of fluorinated materials that improve the thermal stability of LiPF6 electrolyte through the elimination of existing HF and suppression of additional formation.

Designing Nonflammable Liquid Electrolytes for Safe Li-Ion Batteries.

Li-ion batteries are essential technologies for electronic products in the daily life. However, serious fire safety concerns that are closely associated with the flammable liquid electrolyte remains a key challenge. Tremendous effort has been devoted to designing nonflammable liquid electrolytes. It is critical to gain comprehensive insights into nonflammability design and inspire more efficient approaches for building safer Li-ion batteries. This review presents current mechanistic understanding of safety issues and discusses state-of-the-art nonflammable liquid electrolytes design for Li-ion batteries based on molecule, solvation, and battery compatibility level. Various safety test methods are discussed for reliable safety risk evaluation. Finally, the challenges and perspectives of the nonflammability design for Li-ion electrolytes are summarized.

Base-Driven Ring-Opening Reactions of Vinylene Carbonate

Vinylene carbonate (VC) is the most commonly applied performance-enhancing electrolyte additives in Li-ion batteries to date. Despite numerous studies, there is a lack of consensus regarding the various reaction pathways of VC and their implications. VC has primarily been observed to either polymerize forming poly(vinylene carbonate) (poly(VC)) or decompose releasing major amounts of CO2, two seemingly contradictory processes. Herein, we present evidence of additional reaction pathways of VC highlighting its role as a H2O scavenging agent. In contrast to the typical electrolyte solvent ethylene carbonate, VC reacts much more rapidly with water impurities, especially when in contact with hydroxides, forming products less likely to influence cell performance. Efficient removal of water and hydroxides is essential to preserve the stability of Li-ion electrolyte solvent and salt, hence guaranteeing a long lifetime of the battery. Model studies pinpointing reaction pathways of electrolytes and additives, as presented herein, are critical not only to improve modern Li-ion cells but also to establish design principles for future battery chemistries.

Asymmetric transition of electrical resistance in an all-solid-state redox device with Fe3O4 and Li-ion electrolyte thin films for physical reservoir computing

In recent years, ion-gating devices have been used in artificial neuromorphic computing and achieved high performance for time-series data processing. However, the origin of this performance still needs to be clarified. In this study, we fabricated an all-solid-state redox device with functional material Fe3O4 and Li-ion conducting solid electrolytes, and the transient response of the electrical resistance of the Fe3O4 thin film to time-series data input was investigated. The transition between high and low electrical resistance states was asymmetric, and residual Li-ion in the thin film led to a hysteresis effect. These unique features, which are induced by ion-electron dynamics coupling, contributes to the high performance of physical reservoir computing utilizing an ion-gating device.

A three-electrode dual-power-supply electrochemical pumping system for fast and energy efficient lithium extraction and recovery from solutions

The demand for Li-ion batteries (LIBs) for use in electric vehicles, which is key to realizing a decarbonized society, is accelerating. However, the supply of Li resources has recently become a major issue, thereby necessitating the development of economical and sustainable technologies of brine/seawater-based Li extraction and recycling Li from spent LIBs. This paper presents an innovative electrochemical pumping technology based on a new cell structure for Li extraction/recovery. This system can provide large electrochemical driving forces while preventing the occurrence of electronic conduction due to electrolyte reduction. This electrochemical pumping system allows extraction/recovery of Li ions from the anode side to the cathode side, rather than the diffusion of other ions, due to the ion-diffusion-bottleneck size of the electrolyte material. Using this system, high-purity Li can be collected with high energy efficiency and at least 464 times faster than that via conventional electrochemical pumping, even with a commercially available Li-ion electrolyte plate.

Electrochemical Investigations of Sulfur-Decorated Organic Materials as Cathodes for Alkali Batteries.

Alkali metal-sulfur batteries (particularly, lithium/sodium- sulfur (Li/Na-S)) have attracted much attention because of their high energy density, the natural abundance of sulfur, and environmental friendliness. However, Li/Na-S batteries still face big challenges, such as limited cycle life, poor conductivity, large volume changes, and the "shuttle effect" caused by the high solubility of Li/Na-polysulfides. Herein, novel organosulfur-containing materials, i.e., bis(4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS-OH) and 2,4-thiophene/arene copolymer (TAC) are proposed as cathode materials for Li and Na batteries. BiTEMPS-OH shows an initial discharge/charge capacity of 353/192mAhg-1 and a capacity of 62mAhg-1 after 200 cycles at 100mAg-1 in ether-based Li-ion electrolyte. Meanwhile, TAC has an initial discharge/charge capacity of 270/248mAhg-1 and better cycling performance (106mAhg-1 after 200 cycles) than BiTEMPS-OH in the same electrolyte. However, the rate capability of TAC is limited by the slow diffusion of Li-ions. Both materials show inferior electrochemical performances in Na battery cells compared to the Li analogs. X-ray powder diffraction reveals that BiTEMPS-OH loses its crystalline structure permanently upon cycling in Li battery cells. X-ray photoelectron spectroscopy demonstrates the cleavage and partially reversible formation of S-S bonds in BiTEMPS-OH and the formation/decomposition of thick solid electrolyte interphase on the electrode surface of TAC.

Recent Advancements in Li-ion Batteries Electrolytes: A Review

Recent Advancements in Li-ion Batteries Electrolytes: A Review

Reaction kinetics of lithium-sulfur batteries with a polar Li-ion electrolyte: modeling of liquid phase and solid phase processes.

The present investigation fits the reaction kinetics of a lithium-sulfur (Li-S) battery with polar electrolyte employing a novel two-phase continuum multipore model. The continuum two-phase model considers processes in both the liquid electrolyte phase and the solid precipitates phase, where the diffusion coefficients of the Li+ ions in a solvent-softened solid state are determined from molecular dynamics simulations. Solubility experiments yield the saturation concentration of sulfur and lithium sulfides in the polar electrolyte employed in this study. The model describes the transport of dissolved molecular and ion species in pores of different size in solvated or desolvated form, depending on pore size. The Li-S reaction model in this study is validated for electrolyte 1 M LiPF6 in EC/DMC. It includes seven redox reactions and two cyclic non-electrochemical reactions in the cathode, and the lithium redox reaction at the anode. Electrochemical reactions are assumed to take place in the electrolyte solution or the solid state and cyclic reactions are assumed to take place in the liquid electrolyte phase only. The determination of the reaction kinetics parameters takes place via fitting the model predictions with experimental data of a cyclic voltammetry cycle with in operando UV-vis spectroscopy.

Alkyl Dicarbonate-Based Electrolytes Can Enable Long-Lived Li-Ion Cells at High-Temperatures

Alkyl dicarbonates are known electrolyte degradation products produced in Li-ion cells that use ethylene carbonate (EC) and dimethyl carbonate (DMC) as electrolyte components. Also referred to as dimerization compounds, dimethyl 2,5-dioxahexanedioate (DMOHC) and diethyl 2,5-dioxahexanedioate (DEOHC), were investigated as a possible sole electrolyte solvent or and one component of a blended solvent mixture, when mixed with linear carbonates. The viscosities of DMOHC and DEOHC were measured in this report and compared to the predictions of the Advanced Electrolyte Model1, along with the two alkyl dicarbonates mixed with lithium salts and other common electrolyte solvents. Electrolytes based on DMOHC or DEOHC alone exhibit much higher viscosity than conventional EC-based electrolytes at room temperature. Thus, for testing, LiNi0.5Mn0.3Co0.2O2/graphite (NMC532), LiNi0. 83Mn0. 6Co0. 11O2/graphite (Ni83) and LiFePO4(LFP)/graphite cells with DMOHC were tested at 70°C and 85°C using C/20 charge and discharge rates.DMOHC and DEOHC were mixed with two different electrolyte salts. First, the common LiPF6 salt and the second, lithium bis(fluorosulfonyl)imide (LiFSI), both with 2% vinylene carbonate (VC). These two electrolytes were tested in NMC532/graphite cells cycled to 4.3V at a C/20 charge/discharge rate and 70°C. Cells with DMOHC and LiFSI showed considerable improvements in capacity retention compared to those filled with an EC-based electrolyte with LiPF6 salt, also cycled at 70°C. The same conclusion was found with NMC532 cells filled with DEOHC with LiFSI salt or LiPF6. Figure 1a shows the fractional capacity versus time for NMC532/graphite, Ni83/graphite and LFP/graphite pouch cells with 1.0 M LiFSI in DMOHC with 2% VC (vinylene carbonate) and 1% DTD (ethylene sulfate) additives tested at C/20 and 85°C. These cells were tested to upper cut-off potentials of 3.8, 3.9 and 3.65 V respectively. In addition, Figure 1b shows the corresponding voltage polarization results. Results show that Ni-containing cells experience exceptional lifetimes and low impedance growth despite the high cycling temperature. DMOHC-containing cells have since been tested up to 100°C. DMOHC was most advantageous for mitigating severe gassing at high temperatures. Ex-situ gas experiments show DMOHC-containing Ni83 cells produce the least amount of gas even at high voltage (4.0 V) compared to cells using EC-based electrolytes. Ni-containing cells operating to low voltage limits show unprecedented cycling lifetimes when using DMOHC electrolytes containing LIFSI while also exhibiting limited gassing. To mitigate the high viscosity of DMOHC, various cells were filled with electrolytes that used DMOHC and various percentages of diethyl carbonate (DEC) and dimethyl carbonate (DMC) with LiFSI as the salt. DMC/DEC was chosen for its low viscosity and its ionic conductivity. Even with DMC, the cycling performance showed improvements over traditional EC-based electrolytes. There were slight decreases in performance compared to a cell with a pure DMOHC electrolyte. In addition, various additives were tested, including prop-1-ene-1,3-sultone (PES), to see if gassing could be further limited. We propose DMOHC and DEOHC as new solvents for Li-ion cell electrolytes, possibly replacing EC, to enable long-lasting, high-temperature tolerant Li-ion cells. REFERENCES E. R. Logan, E. M. Tonita, K. L. Gering, and J. R. Dahn, J Electrochem Soc, 165, A3350–A3359 (2018). Figure 1. (a) Normalized capacity versus time for LFP (blue), NMC532 (red) and Ni83 (black) artificial graphite cells, using 1M LIFSI DMOHC 2%VC 1%DTD electrolyte cycling at C/20 and at 85°C. (b) corresponding voltage polarization data versus time. Figure 1

Nitrile-functionalized Poly(siloxane) as Electrolytes for High-Energy-Density Solid-State Li Batteries.

In the quest to replace liquid Li-ion electrolytes with safer and non-toxic solid counterparts for Li-ion batteries, polysiloxane polymers have attracted considerable attention as they offer low glass transition temperatures, stability with metallic lithium, and versatility in chemical functionalization of the backbone. Herein, we present the synthesis of Li-ion conductive polysiloxane-based polymers functionalized with 60% nitrile groups per chain unit. The synthesis procedure is based on the reaction of poly(dimethylsiloxane-co-methylvinylsiloxane) polymer with 2-cyanoethanethiol, followed by the addition of lithium bis(trifluoromethanesulfonyl)imide. The presented polysiloxane-based polymers exhibit exceptionally high ionic conductivity up to 0.375 mS cm-1 at 60 °C and Li+ ion transfer number of 0.73, one of the highest reported for polymer Li-ion conducting electrolytes. Their electrochemical performance was evaluated in both symmetrical and full-cell configurations to test the utility of synthesized polymers as electrolytes in Li-ion batteries.

A Short Review of Li-ion Battery Materials: Recent Advancements and Research Gaps

This review explores the current state of research on lithium-ion (Li-ion) battery materials, with a focus on key findings and research gaps. Li-ion batteries have revolutionized the portable electronics and electric vehicle industries, but their performance and safety still face challenges. This review discusses the major components of Li-ion batteries, including cathode, anode, electrolyte, and separator materials, and evaluates recent developments and limitations in each category. It also discusses the prospects and emerging trends in Li-ion battery material research. The review aims to provide insights into the state of the art, highlight areas where further research is needed, and contribute to the ongoing efforts to advance Li-ion battery technology.

A Short Review of Li-ion Battery Materials: Recent Advancements and Research Gaps

This review explores the current state of research on lithium-ion (Li-ion) battery materials, with a focus on key findings and research gaps. Li-ion batteries have revolutionized the portable electronics and electric vehicle industries, but their performance and safety still face challenges. This review discusses the major components of Li-ion batteries, including cathode, anode, electrolyte, and separator materials, and evaluates recent developments and limitations in each category. It also discusses the prospects and emerging trends in Li-ion battery material research. The review aims to provide insights into the state of the art, highlight areas where further research is needed, and contribute to the ongoing efforts to advance Li-ion battery technology.

Alkyl Dicarbonates, Common Electrolyte Degradation Products, Can Enable Long-Lived Li-Ion Cells at High Temperatures

A common degradation product dimethyl-2,5-dioxahexane carboxylate (DMOHC) produced in Li-ion cell electrolytes after ageing is used here as an electrolyte solvent, allowing Li-ion cells to operate at high temperatures (70 °C and 85 °C) with excellent capacity retention and low impedance growth. Viscosity and conductivity values are reported for various DMOHC and diethyl-2,5-dioxahexane carboxylate (DEOHC) blends with dimethyl carbonate (DMC) and diethyl carbonate (DEC). Charge-discharge cycling data are reported for LiFePO4/graphite (LFP), Li[Ni0.5Mn0.3Co0.2]O2/graphite (NMC3.8 V, balanced for 3.8 V cut-off), Li[Ni0.6Mn0.4Co00]O2/graphite (NMC640, balanced for 4.1 V cut-off) and Li[Ni0.83Mn0.06Co0.11]O2/graphite (Ni83, balanced for 4.06 V cut-off) pouch cells at 70 °C and 85 °C. Pouch cells with DMOHC electrolyte have extraordinarily long lifetimes at 70 °C and 85 °C Pouch cells containing DMOHC-based electrolytes produce little to no gas compared to traditional ethylene carbonate (EC) based electrolytes. Cells taken apart after testing showed uniform negative electrode lithiation and no differences in the cell components were observed when using DMOHC electrolytes compared to EC. Lastly, micro X-ray fluorescence spectroscopy analysis was performed to probe the degree of transition metal deposition on negative electrodes of cycled cells. Very low levels of transition metals were found on the negative electrode even for cells tested at 85 °C. DMOHC is a co-solvent that can enable Li-ion batteries with exceptional high temperature lifetimes.

Characterising the Ionic Transport and Thermodynamic Properties of Potassium-Ion Electrolytes

The lithium price has increased more than sevenfold since the start of 2021 (as of May 2022), reaching unprecedented price levels and demonstrating significant challenges for the security of supply of lithium for lithium-ion batteries (LIBs)1. With forecasts showing a potential significant lithium supply deficit by 20301, the case for alternative chemistries based on abundant minerals which can fulfil some LIB functions has never been stronger. Sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) are emerging as promising complementary technologies to lithium-ion batteries (LIBs) due to the availability and low cost of sodium and potassium, and the minerals comprising their leading electrodes2 , 3. KIBs have a significant advantage over NIBs as K+ can reversibly intercalate into the graphite electrodes used in LIBs, thus one of the primary components of KIBs is already available at commercial scale, unlike for NIBs2. The lower charge density of K+ compared to Li+ has also been suggested to result in superior ion transport in the electrolyte with KIBs potentially able to deliver superior rate capability and low-temperature performance. However, a comprehensive characterisation of the ionic transport and thermodynamic properties of nonaqueous K-ion electrolytes, critical to the development of KIBs, has not yet been reported. Here, for the first time, we fully characterise the ionic transport and thermodynamic properties of a nonaqueous K-ion electrolyte4, potassium bis(fluorosulfonyl)imide (KFSI) in 1,2-dimethoxyethane (DME) and compare it with its Li-ion equivalent (LiFSI in DME) over the concentration range 0.25–2 m. This was realised by developing a K metal preparation protocol enabling sufficient K metal stability for electrolyte characterisation. Our results demonstrate that the K-ion electrolyte indeed displays significantly higher salt diffusion coefficients and transference numbers than the Li-ion electrolyte, evidencing the potential for high-power applications of KIBs. IEA. Global EV Outlook 2022. (IEA, 2022).Dhir, S., Wheeler, S., Capone, I. & Pasta, M. Outlook on K-Ion Batteries. Chem vol. 6 2442–2460 (2020). doi: 10.1016/j.chempr.2020.08.012Hosaka, T., Kubota, K., Hameed, A. S. & Komaba, S. Research Development on K-Ion Batteries. Chem. Rev. acs.chemrev.9b00463 (2020) doi:10.1021/acs.chemrev.9b00463.Dhir, S., Jagger, B., Maguire, A. & Pasta, M. Characterising the Ionic Transport and Thermodynamic Properties of Potassium-ion Electrolytes. Res. Sq. (2022) doi:10.21203/RS.3.RS-2310020/V1. Figure 1