Electrolytes For Lithium Batteries Research Articles

Advancements in Polyethylene Oxide (PEO)–Active Filler Composite Polymer Electrolytes for Lithium-Ion Batteries: A Comprehensive Review and Prospects

Polyethylene oxide (PEO) has become a highly sought−after polymer electrolyte for lithium−ion batteries (LIBs) due to its high ionic conductivity, strong mechanical properties, and broad electrochemical stability range. However, its usefulness is hindered by its limited ionic conductivity at typical temperatures (<60 °C). Many researchers have delved into the integration of active fillers into the PEO matrix to improve the ionic conductivity and overall efficiency of composite polymer electrolytes (CPEs) for LIBs. This review delves deeply into the latest developments and insights in CPEs for LIBs, focusing on the role of PEO–active filler composites. It explores the impact of different types and morphologies of active fillers on the electrochemical behavior of CPEs. Additionally, it explores the mechanisms that contribute to the improved ionic conductivity and Li−ion transport in PEO−based CPEs. This paper also emphasizes the present obstacles and prospects in the advancement of CPEs containing PEO–active filler composites for LIBs. It serves as a valuable reference for scientists and engineers engaged in the domain of advanced energy storage systems, offering insights for the forthcoming development and enhancement of CPEs to achieve superior performance in LIBs.

Real-time monitoring the formation of polymer double network for gel polymer electrolyte by means of dielectric spectroscopy

A non-destructive method of detecting the internal information of the system is attempted in a polymer double network for gel polymer electrolyte in lithium-ion battery. The real-time monitoring for polymerization of 1,3-dioxolane (DOL) and cross-linking of cyanoethyl poly(vinyl alcohol) (PVA-CN) is carried out in a coin cell at 0–80 ℃ by means of dielectric spectrum. A widely distributed dielectric relaxation varying with monitoring time and temperature is observed in the frequency range of 3–103 kHz, and the relaxation parameters of the three sub-relaxations are obtained by fitting the dielectric spectrum with the HN equation. It is found that the relaxation intensity Δε and relaxation time τ are obviously dependent on the monitoring time and temperature: Δε and τ change obviously near the respective gel points of DOL and PVA-CN (DOL at 25 ℃, PVA-CN at 60 ℃), suggesting gelation at two gel points respectively. The different structural changes of the system before and after gelling temperature are speculated, and the possible microstructure of the system in each temperature range is proposed after analyzing the relaxation parameters. The applicability of the real-time dielectric monitoring in the study of the structure of gel polymer electrolytes is preliminarily concluded.

Recovery of lithium from spent NMC batteries through water leaching, carbothermic reduction, and evaporative crystallization process

The demand for lithium grows exponentially due to its expanding range of applications. Because of their composition, spent lithium-ion batteries represent a promising secondary source of lithium. The present work focuses on a two-stage lithium recovery process applied to two different black masses from NMC 622 electric vehicle batteries after prior crushing and separation stages. In the first stage, hydrolysis is used to extract lithium compounds from the degradation products of the electrolyte (LiPF6). In the second stage, a carbothermic reduction process is carried out in which various reducing agents are evaluated. The result of this stage is a product that is leached with water and crystallised by evaporation. The result of the first stage is two industrially useful compounds: LiF, which is used in the production of lithium-ion battery electrolytes, and Li3PO4, which is used in the production of lithium-iron-phosphate batteries. In the second stage, Li2CO3 is recovered with a remarkably low LiF content, with a purity higher than 98.4 %. This process allows 90–94 % of the total lithium in the black mass to be recovered.

Exploring the Relationship between Interfacial Chemistry and Thermal Safety of a Flame Retarding Semisolid Electrolyte

The safety-related performance of LIBs still remains as a major issue even after more than three decades of commercialization.1 When typical electrolytes composed of flammable organic liquid solvents vaporize and decompose exothermically during thermal runaway, they pose serious risk to human health and infrastructure.2 Conventional lithium-ion batteries (LIBs) are energy storage devices which function as electrochemical systems subject to highly dynamic heterogeneous reaction phenomena. As a result, the tolerance levels of tangible harm to users and surrounding environments may be amplified considerably as scale and pervasiveness of technology increases. Beyond consumer devices, large-scale energy storage to complement renewable power generation technologies is instrumental to the goal of decarbonization via electrification and thus global goals for carbon neutrality in the 21st century. Renewable power generation benefits substantially from decoupling the spatial and temporal points of energy generation from that of demand.Recent efforts in academia and industry alike have endeavored to replace volatile and flammable conventional liquid electrolytes (composed of classes of compounds such as carbonates or ethers) with intrinsically nonflammable liquid electrolytes (composed of fluorinated and phosphorus-containing organic solvents).3–5 Simultaneously, solid-state electrolytes have been touted as an avenue to not only wholly replace the liquid component of the cell to improve safety, but also as a higher-energy density next-generation battery electrolyte.6 However, these strategies are often examined as materials-level design choices for improving “built-in” safety and not as changes to a dynamic and multiscale electrochemical system.In this study, we find that the intrinsic safety of a system is highly dependent on the interfacial degradation pathways of the electrode-electrolyte configuration, which acts as a direct complement to the thermal behavior which may result in thermal runaway. Through detailed multimodal calorimetry and characterization of the interfacial composition, this work subsequently brings the question of flammability into focus as a downstream consequence of the interfacial reaction kinetics. This is accomplished through the combined efforts of thermal analyses as well as X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy accompanied with electron crystallography analyses, and nuclear magnetic resonance studies of the ionic transport behavior through the polymeric electrolyte. Through these efforts, design principles centered around holistic assessment of the lifespan of materials and their electrochemical and thermal interactions are developed towards the greater goal of improving the safety and resilience of LIBs and their devices against the wide spectrum of abuse scenarios created by their expanding application space.(1) Feng, X.; Ren, D.; He, X.; Ouyang, M. Mitigating Thermal Runaway of Lithium-Ion Batteries. Joule 2020, 4 (4), 743–770. https://doi.org/10.1016/j.joule.2020.02.010.(2) Wang, Q.; Jiang, L.; Yu, Y.; Sun, J. Progress of Enhancing the Safety of Lithium Ion Battery from the Electrolyte Aspect. Nano Energy 2019, 55, 93–114. https://doi.org/10.1016/j.nanoen.2018.10.035.(3) Cao, X.; Xu, Y.; Zhang, L.; Engelhard, M. H.; Zhong, L.; Ren, X.; Jia, H.; Liu, B.; Niu, C.; Matthews, B. E.; Wu, H.; Arey, B. W.; Wang, C.; Zhang, J.-G.; Xu, W. Nonflammable Electrolytes for Lithium Ion Batteries Enabled by Ultraconformal Passivation Interphases. ACS Energy Letters 2019. https://doi.org/10.1021/acsenergylett.9b01926.(4) Wang, J.; Yamada, Y.; Sodeyama, K.; Watanabe, E.; Takada, K.; Tateyama, Y.; Yamada, A. Fire-Extinguishing Organic Electrolytes for Safe Batteries. Nat Energy 2018, 3 (1), 22–29. https://doi.org/10.1038/s41560-017-0033-8.(5) Zheng, Q.; Yamada, Y.; Shang, R.; Ko, S.; Lee, Y.-Y.; Kim, K.; Nakamura, E.; Yamada, A. A Cyclic Phosphate-Based Battery Electrolyte for High Voltage and Safe Operation. Nat Energy 2020, 5 (4), 291–298. https://doi.org/10.1038/s41560-020-0567-z.(6) Janek, J.; Zeier, W. G. A Solid Future for Battery Development. Nat Energy 2016, 1 (9), 1–4. https://doi.org/10.1038/nenergy.2016.141

Polymerized Acrylonitrile Artificial SEI for Long-Life Li-Metal Battery and Enhanced Stability for Li/Li10GeP2S12 Interface

Lithium metal anode batteries have attracted significant attention as a promising energy storage technology, offering a high theoretical specific capacity and low electrochemical potential. Utilizing lithium metal as the anode material can substantially increase energy density compared to conventional lithium-ion batteries. However, the practical application of lithium metal anodes has encountered notable challenges, primarily due to the formation of dendritic structures during cycling. These dendrites pose safety risks and degrade battery performance. Addressing these challenges necessitates the development of a reliable and effective protection layer for lithium metal. This study presents a cost-effective and convenient method to produce lithium metal protective layers by creating ex-situ polymer layers using acrylonitrile (AN). This method extends the lifetime of lithium metal anodes by a remarkable factor of six under high current (1 mA/cm²) cycling conditions. While the cycle life of bare lithium metal is approximately 150 hours under high current conditions, AN-treated lithium metal anodes exhibit an impressive longevity of over 900 hours.Furthermore, with the increasing attentions on solid-state electrolytes – which address the safety concerns and energy density limitations associated with conventional liquid electrolytes in lithium-ion batteries, the interface between Li metal and solid-state electrolytes has been the major challenges. For example, Li10GeP2S12 (LGPS) stands out among these solid electrolyte materials, boasting high ionic conductivity (1 x 10⁻² S cm⁻¹). Nonetheless, the severe instability of the interface between lithium metal anodes and solid electrolytes, including dendrite formation and electrolyte degradation, hindering their practical implementation. This work also goes deeply to explore the stability and performance of Li | LGPS systems by utilizing a polymerized acrylonitrile interfacial. By elucidating the mechanisms governing the interfacial layers, this low-cost fabrication of AN-treated lithium metal holds significant potential for advancing the commercialization of future lithium-metal batteries, surpassing the capabilities of traditional lithium-ion batteries.

Computational and Experimental Study of a Sustainable Lithium Acetate and Urea-Based Electrolyte for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are the most widely used energy storage systems in portable devices, electric vehicles, large-scale energy storage power, and other applications. The optimal performance and safety of LIBs are mainly determined by the electrolyte, which facilitates the transport of Li+ ions and promotes the formation of the SEI layer. Since commercial LIBs are predominantly composed of organic-based electrolytes, these present elevated costs, safety risks, and environmental hazards due to their elevated flammability and fluorinated composition. To address these concerns, aqueous electrolytes have been explored as safer alternatives to organic solvents. However, the use of aqueous LIB electrolytes is restricted due to the narrow electrochemical stability window of water (ESWH2O ≈ 1.23 V). This problem is usually overcomed by using superconcentrated electrolytes, including "water-in-salt" and "water-in-bisalt," which extend the ESW. However, their practicality remains uncertain due to the high concentration of fluorinated salts, which leads to increased cost and toxicity.1 In this study, we employed computational and experimental methods to investigate the use of non-fluorinated aqueous electrolytes prepared by combining different ratios of LiCH3COOH and a water-urea mixture of fixed composition (LiCH3COO-H2O-CO(NH2)2) for their use as an electrolyte for LIBs. ESWs were determined by cyclic voltammetry using GCE, Pt, and Al as working electrodes. The electrolyte with the highest ESW (3.2 V) was probed to be compatible with commercial electrodes such as TiO2, LTO, LMO, and LFP, and was used to assemble a LIB cell with LTO and LMO as electrodes. This cell presented an average output voltage of 2.3 V and a specific capacity of 105 mAh/g over 200 cycles at a current density of 0.5 A/g. Furthermore, the thermodynamic and kinetic factors associated with the electrochemical stability of the electrolyte have been studied using DFT and molecular dynamics (MD), respectively. Adiabatic redox potentials of the electrolyte species obtained by DFT show calculated ESWs higher than 4.5 V. Transport properties of the species in the electrolyte were studied via molecular dynamics and these show that the diffusion of Li+ is comparable to the diffusion observed in organic electrolytes.2 Structurally, we also observed that urea disrupts the Li-water structure, leading to a decrease in the coordination number of water molecules to Li+ (CNLi-H2O = 1.4). This result has been experimentally confirmed using NIR and Raman spectroscopy. Overall, these results demonstrate the effectiveness of employing a lithium acetate-urea-based aqueous electrolyte as an alternative to organic electrolytes for the development of more secure, environmentally friendly, and sustainable LIBs.1. Brown, J.; Grimaud, A. With Only a Grain of Salt. Nat. Energy 2022, 7 (2), 126–127.2. Galvez-Aranda, D. E.; Seminario, J. M. Ion Pairing, Clustering and Transport in a LiFSI-TMP Electrolyte as Functions of Salt Concentration Using Molecular Dynamics Simulations. J. Electrochem. Soc. 2021, 168 (4), 040511.

Deep Learning Based 3D Resolution Recovery for Breakthrough Imaging of Electrochemical Energy Devices

Many energy materials can only be understood within the context of the (often sealed) devices they make up. Batteries and fuel cells contain intricate mixtures of materials with features and arrangements that span across many orders of magnitude in size and operate under non-ambient conditions. In these devices, the microstructures of the constituent materials and how they are arranged with respect to each other is directly linked to the device performance and degradation behaviors. Complicating matters, opening the devices for inspection and analysis can irreversibly alter the very microstructures in question and can pose safety hazards to researchers if not done correctly. Furthermore, critical material and device properties such as tortuosity or ion transport pathways can only be accurately quantified in 3D. As such, observing microstructures and their evolution in 3D and in their native state is essential for developing a robust understanding of how to engineer new battery and fuel cell materials and architectures with improved performance.X-ray microscopy (XRM) provides a unique method for observing these microstructures in 3D at high resolutions without needing to open them. However, microscopy techniques like XRM make tradeoffs between FOV and resolution, which can pose challenges for strongly multiscale systems like batteries and fuel cells. For example, if images are acquired at high enough resolution to observe critical features like electrode particle sizes in lithium-ion batteries or gas diffusion layer fiber weaves, catalyst distributions, and microporous layer cracks in polymer electrolyte fuel cells, the field of view of that image is restricted to a small local region of the sample. This means that broader defect distributions or larger scale inhomogeneities will be missed. Additionally, for quantitative analysis applications, this means that statistical relevance will be sacrificed because of the limited analysis volume at the appropriate resolution. And for computational modelling efforts, device level phenomena will not be captured well due to the restricted field of view.Advances in modern AI-based resolution recovery methods combined with the non-destructive multiscale imaging capabilities of X-ray microscopy have allowed researchers to overcome this dependency between resolution and field of view to produce 3D images with both high resolution and large field of view. We present here examples of applying these methods to applications in lithium-ion battery and polymer electrolyte fuel cell research [1].[1] Wang, Y.D., Meyer, Q., Tang, K. et al. Large-scale physically accurate modelling of real proton exchange membrane fuel cell with deep learning. Nat Commun 14, 745 (2023).

Improving Room Temperature Performance of All-Solid-State Polymer Batteries through Cell Activation

Solid polymer electrolytes (SPE) are gaining increasing attention for use in all-solid-state lithium batteries (ASSLB) due to their enhanced safety and simplified processing.[1] However, their conventional operation requires elevated temperatures.[2, 3] Here, we propose a straightforward hot-press activation method to facilitate cell operation at room temperature (r.t., 30 °C) for SPE-based ASSLB. This activation method induces grain amorphization, leading to a substantial reduction in grain boundary resistance within the SPE and achieving a fourfold increase in r.t. ionic conductivity. Furthermore, by decoupling Li-ion transport processes, the activation significantly diminishes the electrode-electrolyte interfacial resistances for both the cathode and anode, thereby enhancing kinetics and overall cell performance at r.t.. Through the application of an optimized activation procedure, all-solid-state LiFeO4 (LFP)|SPE|Li cells exhibit noteworthy performance enhancements, demonstrating both high specific capacity and stable cycling at r.t.References Mauger, A., et al., Building Better Batteries in the Solid State: A Review. Materials, 2019. 12(23).Chen, R.J., et al., The pursuit of solid-state electrolytes for lithium batteries: from comprehensive insight to emerging horizons. Materials Horizons, 2016. 3(6): p. 487-516.Mindemark, J., et al., Beyond PEO—Alternative host materials for Li + -conducting solid polymer electrolytes. Progress in Polymer Science, 2018. 81: p. 114-143.

Argyrodite–Li6PS5cl/Polymer–Based Highly Conductive Composite Electrolyte for All–Solid–State Batteries

The intense focus of research is on all–solid–state lithium–ion batteries (ASSLBs) with solid electrolytes (SEs) owing to their potential qualities such as high energy, high power density, and enhanced safety compared to conventional Lithium Ion batteries (LIBs).1 In spite of the numerous advantages of ASSLBs, a lot of issues still need to be solved before commercialization.2 Typically, SEs demonstrate lower ionic conductivity (σ) compared to liquid electrolytes.1 For instance, lithium phosphorous oxynitride (LiPON), a frequently employed SE, exhibits an σ of ca. 10–6 S/cm. In contrast, a liquid electrolyte like lithium hexafluorophosphate in ethylene carbonate and propylene carbonate demonstrates a higher σ of ca. 10–2 S/cm at room temperature.1 So far, extensive research has been conducted on Argyrodite–Li6PS5Cl (LPSCl) electrolytes, yielding promising results for their applications in Li–ion and Li–S batteries.3However, a significant challenge in using argyrodite LPSCl in ASSLBs applications is the interface instability between the LPSCl and electrodes. During charge-discharge (CD) cycling, LPSCl tends to oxidize, leading to the production of elemental sulfur, polysulfides, phosphates, and lithium chloride at the electrode interface.3These side products ultimately hinder cycling stability and can result in dendrite formation at the interface. Another important drawback of LPSCl is its non–negligible electronic conductivity, which allows for smooth electron transport through the LPSCl electrolyte.4Consequently, Li dendrites can be directly deposited at the grain boundaries of LPSCl particles, leading to a serious self–discharge issue.4 In this study, we have developed a composite electrolyte of LPSCl/polymer to enhance the contact between the electrolyte and electrodes and suppress dendrite formation at the grain boundary of the LPSCl ceramic. The monomer, triethylene glycol dimethacrylate (TEGDMA), is utilized for in–situ polymerization through thermal curing to create the Argyrodite LPSCl/polymer composite electrolyte. Additionally, the ball–milling technique was employed to modify the morphology and particle size of the LPSCl ceramic. The ball–milled LPSCl/polymer composite electrolyte (BLPSCl–P) demonstrates slightly higher ionic conductivity (ca. 2.21 × 10–4 S/cm) compared to the as–received LPSCl/polymer composite electrolyte (ALPSCl–P) (ca. 1.65 × 10–4 S/cm) at 25 °C (Figure 1). Furthermore, both composite electrolytes exhibit excellent compatibility with Li–metal and display cycling stability for up to 1000 hours (375 cycles) (Figure 1), whereas the as–received LPSCl (ALPSCl) and ball–milled LPSCl (BLPSCl) electrolytes maintain stability for up to 600 hours (225 cycles) at a current density of 0.4 mA/cm2. The SSB with the BLPSCl–P delivers high specific discharge capacity (138 mAh/g), Coulombic efficiency (99.97%), and better capacity retention at 0.1C, utilizing the battery configuration of coated NMC811//electrolyte//Li–Indium (In) at 25 °C. Figure 1 REFERENCES (1) Li, S.; Zhang, S. Q.; Shen, L.; Liu, Q.; Ma, J. Bin; Lv, W.; He, Y. B.; Yang, Q. H. Progress and Perspective of Ceramic/Polymer Composite Solid Electrolytes for Lithium Batteries. Adv. Sci. 2020, 7 (5).(2) Lee, S. E.; Sim, H. T.; Lee, Y. J.; Hong, S. B.; Chung, K. Y.; Jung, H. G.; Kim, D. W. Li6PS5Cl–Based Composite Electrolyte Reinforced with High–Strength Polyester Fibers for All–Solid–State Lithium Batteries. J. Power Sources 2022, 542 (6), 231777. (3) Lee, Y. G.; Fujiki, S.; Jung, C.; Suzuki, N.; Yashiro, N.; Omoda, R.; Ko, D. S.; Shiratsuchi, T.; Sugimoto, T.; Ryu, S.; Ku, J. H.; Watanabe, T.; Park, Y.; Aihara, Y.; Im, D.; Han, I. T. High–Energy Long–Cycling All–Solid-State Lithium Metal Batteries Enabled by Silver–Carbon Composite Anodes. Nat. Energy 2020, 5 (4), 299–308.(4) Yang, X.; Gao, X.; Jiang, M.; Luo, J.; Yan, J.; Fu, J.; Duan, H.; Zhao, S.; Tang, Y.; Yang, R.; Li, R.; Wang, J.; Huang, H.; Veer Singh, C.; Sun, X. Grain Boundary Electronic Insulation for High–Performance All–Solid–State Lithium Batteries. Angew. Chem. Int. Ed. 2023, 62 (5). Figure 1

(Invited) Fluorinated Linear Carbonate Electrolyte for Lithium-Ion Batteries with Fast-Charging, High Voltage, and Wide Operating Temperatures

Lithium-ion batteries (LIBs) are key solutions to clean energy. Their high energy densities have led to the dominance of LIBs in mobile devices and electric vehicles. However, traditional electrolyte limits their operation at high voltage and extreme environmental temperatures. Here, we designed a new multifunctional electrolyte, in which lithium bis(fluorosulfonyl)imide (LiFSI) is used as salt and fluorinated diethyl carbonate (DFDEC) is used as the major solvent. With this optimized electrolyte, the graphite||LiNi0.8Mn0.1Co0.1O2 (NMC811) full cells are capable of fast-charging and can deliver long-term cycling with a cutoff voltage as high as 4.5V. Specifically, the battery shows the capacity retention of 84.3% after 500 cycles with an average coulombic efficiency (CE) as high as 99.93%. Synchrotron-based characterization suggests the formation of anion derived, LiF-rich interphases on the surfaces of both graphite anode and NMC811 cathode. Thanks to the fast ion transport and stable interphase, the cell in the optimized electrolyte demonstrates stable cycling behavior within a wide operating temperature. At high temperature (60 ºC), the full cell delivers 88.8% of its initial capacity after 130 cycles at a high current density of 1C. At low temperature (-20 ºC), the optimized electrolyte enables a capacity retention of 90.9% after 100 cycles when charging and discharging at 0.2C.Acknowledgment: The work done at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. DOE through Applied Battery Research for Transportation (ABRT) program under contract no. DE-SC0012704. The electrodes used in this study were produced at the U.S. Department of Energy’s (DOE) CAMP (Cell Analysis, Modeling and Prototyping) Facility, Argonne National Laboratory. The CAMP Facility is fully supported by the DOE Vehicle Technologies Office (VTO). This research used beamline 7-ID-2 (SST-2) of the National Synchrotron Light Source II, U.S. DOE Office of Science User Facilities, operated for the DOE Office of Science by Brookhaven National Laboratory under contract number DE-SC0012704. SEM measurements for this manuscript were performed at Center for Functional Nanomaterials, a U.S. DOE office of Science User Facility, at Brookhaven National Laboratory under the contract number DE-SC0012704.

Shear Thickening, Star-Shaped Polymer Electrolytes for Lithium-Ion Batteries.

The safety concerns associated with current lithium-ion batteries are a significant drawback. A short-circuit within the battery's internal components, such as those caused by a car accident, can lead to ignition or even explosion. To address this issue, a polymer shear thickening electrolyte, free from flammable solvents, has been developed. It comprises a star-shaped oligomer derived from a trimethylolpropane (TMP) core and polyether chains, along with the inclusion of 20 wt.% nanosilica. Notably, the star-shaped oligomer serves a dual function as both the solvent for the lithium salt and the continuous phase of the shear thickening fluid. The obtained electrolytes exhibit an ionic conductivity of the order of 10-6 S cm-1 at 20 °C and 10-4 S cm-1 at 80 °C, with a high Li+ transference number (t+ = 0.79). A nearly thirtyfold increase in viscosity to a value of 1187 Pa s at 25 °C and a critical shear rate of 2 s-1 were achieved. During impact, this electrolyte could enhance cell safety by preventing electrode short-circuiting.

Effect of Mechanical Compression on Ionic Conductivity of PEO-LiTFSI Solid Polymer Electrolytes

In the field of energy storage materials, the development of robust solid polymer electrolytes for lithium-ion batteries necessitates an understanding of ionic conductivity when subjected to mechanical stress. Accurate determination of ionic conductivity requires knowing the electrolyte thickness, which is subject to volumetric changes during charging and discharging of solid-state batteries. However, compressive stress reduces the thickness of the electrolyte by an indeterminate amount.This work presents experimental measurements of ionic conductivity as a function of compressive stress, using poly(ethylene oxide) and with bis(trifluoromethane) sulfonimide (PEO-LiTFSI). In this study, we not only measure the stress-strain response of the electrolytes directly, but also monitor the extent of compression during electrochemical impedance spectroscopy (EIS). Compression was applied up to 50% strain for three consecutive cycles, and the typical thickness for the fabricated electrolytes was ~50 µm. EIS testing was performed by using an impedance analyzer, with the electrolyte placed between stainless steel blocking electrodes. Bulk resistance was determined by equivalent circuit modeling of impedance between 100 Hz and 2 MHz. Ionic conductivity κ was calculated from bulk resistance Rb , electrolyte thickness h, and cross-sectional area A, according to the equation κ = h/(Rb·A).In order to measure both stress and deformation simultaneously, a custom positioning stage was engineered to apply prescribed compression. The apparatus has an in-line load cell for force measurements and a laser triangulation sensor for position tracking with submicron resolution. We found that the bulk resistance at room temperature decreases exponentially, with magnitude reduced by approximately five-fold when subjected to compressive stress up to 10 MPa. Beyond ~7 MPa, bulk resistance values were no longer dependent on the amount of applied compression.In addition to mechanical measurements, changes in crystalline and amorphous regions were correlated to the magnitude of compressive stress and the measured ionic conductivity of the electrolyte. For optical imaging with simultaneous EIS measurements, glass slides coated with an indium tin oxide (ITO) film were used instead of stainless steel disks. The extent of crystallinity was visualized by optical microscopy of spherulites through a viewing window when compressed between rigid plates.Figure 1. Apparatus (left) and representative ionic conductivity vs. compressive stress (right) data for a PEO-LiTFSI polymer electrolyte. Figure 1

Impact of Mechanical Stimuli on PEO-Litfsi Stiffness and Ionic Conductivity

Recently a large emphasis has been placed on developing safer electrolytes for lithium-ion batteries as a response to an increase in battery demand. Solid polymer electrolytes, such as those based on polyethylene oxide (PEO) show good resistance to mechanical loading, and when coupled with ceramic fillers demonstrate enhance ionic conductivity as well. Prior to this work, efforts have been made to determine the effects mechanical stimuli have on the stiffness and ionic conductivity of the electrolyte.1–3 However, while previous research has primarily focused on bulk EIS measurements of the electrolyte, here we leverage atomic force microscopy (AFM) to modulate the tip-substrate contact force from a few piconewtons to tens of millinewtons to study the correlation between mechanical loading and ionic conductivity, along with measuring the evolution of the substrate stiffness as a function of mechanical cycling.In this study, we contact the PEO-LiTFSI surface with an electrically conductive Pt-coated tip and mechanically cycle the sample by applying a pre-determined contact force a set number of times. By keeping the contact force and time constant, we extracted the cycle-dependent evolution of the sample stiffness. Results show that stiffness is reduced 30% within the first ten cycles, and then minimally changes with subsequent cycling, matching the results from bulk measurements. Changes in ionic conductivity as a function of mechanical cycling are then measured using electrical characterization techniques. To gain a better understanding of how conductivity and stiffness are evolving, we conducted a parametric study by varying tip size, contact force, and number of mechanical cycles. From early results, we found that electrical resistance increases by ~3% (from 2985 Ohm to 3075 Ohm) after 100 cycles of mechanical force ranging between ~ 0 nN to 450 nN with a 5 µm radius tip. The change in the electrical resistance is believed to originate from the local amorphization of PEO-LiTFSI induced by the mechanical stimuli and resulting change of the local conductivity. These results can be leveraged to further understand how mechanical stimuli affects the mechanical and electrical characteristics of solid electrolytes and help establish a model to predict long-term stability and performance of batteries.This work was supported by the National Science Foundation (#2125640).(1) Yoon, D. et al., ACS Appl. Energy Mater, 6 (18), 9400, 2023(2) Li, X. et al., ACS Appl. Mater. Interfaces, 11 (25), 22745, 2019(3) Liu, L. et al., Nano Energy, 69, 104398, 2020

A Case of Inverted Crosstalk in High-Voltage Lithium-Ion Batteries with Carbonate-Based Electrolytes and LiNi0.5Mn1.5O4 Cathodes

The deployment of spinel LiNi0.5Mn1.5O4 (LNMO) cathodes can be key to develop lithium-ion batteries (LIBs) with higher energy density and lower costs. However, the most common carbonate-based electrolytes for LIBs suffer from severe degradation at high potentials, potentially causing cell failure and safety hazards.[1,2] Therefore, investigating the degradation mechanisms in battery cells employing high-voltage battery cathodes such as LNMO is paramount. In this work [3], we studied the influence of linear carbonates on cycling and interfacial stability. Electrolytes consisting of LiPF6 dissolved in a mixture of cyclic (ethylene carbonate, EC), and linear carbonates (diethyl carbonate, DEC, or dimethyl carbonate, DMC), in a 3:7 EC:DEC/DMC weight ratio, were compared. Galvanostatic cycling and electrochemical impedance spectroscopy data of LNMO||Li cells indicate that the linear carbonate plays a fundamental role in cell failure. Specifically, cells with DEC-based electrolyte show early rollover failure, reaching 80% and 20% state of health at cycle 31 and 55, respectively. In contrast, cells with DMC-containing electrolyte have better stability, keeping 80% state of health until cycle 92, as shown in Figure 1. Three-electrode measurements and further characterizations, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), unveil that cell failure occurs due to instability of the cathode-electrolyte interface; when DEC-based electrolytes are used, a huge impedance build-up is correlated with the formation of a spotty deposit on LNMO particles. In contrast, these deposits are absent in cathodes cycled in the DMC-based electrolyte. These deposits can be explained as originating from electrolyte reduction products forming on the anode side as shown previously for layered oxide||Li cells.[4] Overall, this study provides an insightful discussion on an "inverted crosstalk", i.e., from anode to cathode, degradation mechanism. Importantly, improved cycling stability with DMC compared to DEC is also found for LNMO||graphite cells.[1] V. Nilsson, S. Liu, C. Battaglia, R.-S. Kühnel, Electrochim. Acta 427, 2022, 140867.[2] S. Liu, M. Becker, Y. Huang-Joos, H. Lai, G. Homann, R. Grissa, K. Egorov, F. Fu, C. Battaglia, R.-S. Kühnel, Batteries Supercaps 6, 2023, e202300220.[3] A. Curcio, W. Dachraoui, Ø. Dahl, N. P. Wagner, C. Battaglia, R.-S. Kühnel, submitted.[4] H.-J. Peng, C. Villevieille, S. Trabesinger, H. Wolf, K. Leitner, P. Novák, J. Power Sources 335, 2016, 91-97. Figure 1

Tracking Degradation of Sulfolane-Based Electrolytes in 5 V LNMO Cells

Lithium-ion batteries (LIBs) are today the most used energy storage for portable electronics and electric vehicles – but are laden with concerns of materials scarcity and availability, alongside performance and cost. The development of high-voltage cobalt-free cathode active materials, such as LiNi0.5Mn1.5O4 (LNMO), represents one promising route for next-generation LIBs, due to a combination of high capacity and low cost. Combining LNMO with conventional LIB electrolytes, based on carbonate solvents, however, typically leads to severe capacity fading due to a range of different degradation mechanisms1, not the least due to the high electrochemical potential reached during charge, up to 5 V vs. Li+/Li°.Here we use a range of sulfolane-based electrolytes to improve the stability2 and track the degradation by intermittent current interruption (ICI), which is a rather new protocol to determine the internal resistance of battery cells during cycling3. The ICI data is presented in the form of heat maps, in order to better visualize the variation of internal resistance as function of the cell voltage. Furthermore, Raman spectroscopy is used to identify the decomposition products resulting from the degradation and the data is correlated with the ICI data. Overall this allows us to shine further light on the prospects of sulfolane-based electrolytes for 5 V cells as compared to conventional LIB electrolytes such as e.g. LP40.References Guo, K. et al. High‐Voltage Electrolyte Chemistry for Lithium Batteries. Small Science 2, 2100107 (2022).Xu, J. Critical Review on cathode–electrolyte Interphase Toward High-Voltage Cathodes for Li-Ion Batteries. Nano-Micro Letters vol. 14 (2022).Yin, L. et al. Implementing intermittent current interruption into Li-ion cell modelling for improved battery diagnostics. Electrochim Acta 427, (2022).

Thermodynamic and Kinetic Behaviors of Electrolytes Mediated by Intermolecular Interactions Enabling High-Performance Lithium-Ion Batteries.

Electrolyte solvation chemistry regulated by lithium salts, solvents, and additives has garnered significant attention since it is the most effective strategy for designing high-performance electrolytes in lithium-ion batteries (LIBs). However, achieving a delicate balance is a persistent challenge, given that excessively strong or weak Li+-solvent coordination markedly undermines electrolyte properties, including thermodynamic redox stability and Li+-desolvation kinetics, limiting the practical applications. Herein, we elucidate the crucial influence of solvent-solvent interactions in modulating the Li+-solvation structure to enhance electrolyte thermodynamic and kinetic properties. As a paradigm, by combining strongly coordinated propylene carbonate (PC) with weakly coordinated cyclopentylmethyl ether (CPME), we identified intermolecular interactions between PC and CPME using 1H-1H correlation spectroscopy. Experimental and computational findings underscore the crucial role of solvent-solvent interactions in regulating Li+-solvent/anion interactions, which can enhance both the thermodynamic (i.e., antireduction capability) and kinetic (i.e., Li+-desolvation process) aspects of electrolytes. Additionally, we introduced an interfacial model to reveal the intricate relationship between solvent-solvent interactions, electrolyte properties, and electrode interfacial behaviors at a molecular scale. This study provides valuable insights into the critical impact of solvent-solvent interactions on electrolyte properties, which are pivotal for guiding future efforts in functionalized electrolyte engineering for metal-ion batteries.

Investigation on the thermal runaway mechanism of electrolyte in lithium-ion batteries via ReaxFF molecular dynamics

Lithium-ion batteries have the advantages of high energy density and high cycle times, and have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage. However, lithium-ion batteries are prone to thermal runaway. Subsequently, electrolyte decomposition and combustion occur, leading to an increase in battery temperature and even causing fires or explosions. In order to explore the reaction mechanism of thermal runaway in lithium-ion battery electrolytes, the volatile and combustible organic solvents are selected as the research object. Three different organic solvents were established, namely pure ethylene carbonate (C3H4O3) solvent and its mixture with dimethyl carbonate (C3H6O3) and diethyl carbonate (C5H10O3), respectively. The effect of heating on the thermal runaway of organic solvents was studied using reactive force field molecular dynamics (ReaxFF MD). All three organic solvents will produce a large amount of CH2 free groups and flammable organic substances such as C2H4 during pyrolysis, which is the main reason for thermal runaway of lithium-ion batteries. The research results may contribute to preventing and suppressing thermal runaway in lithium-ion batteries.

Synergistically Engineering Grains and Grain Boundaries toward Li Dendrite-Free Li7La3Zr2O12.

Cation-doped cubic Li7La3Zr2O12 is regarded as a promising solid electrolyte for safe and energy-dense solid-state lithium batteries. However, it suffers from the formation of Li2CO3 and high electronic conductivity, which give rise to an unconformable Li/Li7La3Zr2O12 interface and lithium dendrites. Herein, composite AlF3-Li6.4La3Zr1.4Ta0.6O12 solid electrolytes were created based on thermal AlF3 decomposition and F/O displacement reactions under a high-temperature sintering process. When the AlF3 is thermally decomposed, it leaves Al2O3/AlF3 meliorating the grain boundaries and F- ions partially displacing O2- ions in the grains. Due to the higher electronegativity of F- in the grains and the grain-boundary modification, these AlF3-Li6.4La3Zr1.4Ta0.6O12 deliver optimized electronic conduction and chemical stability against the formation of Li2CO3. The Li/AlF3-Li6.4La3Zr1.4Ta0.6O12/Li cell exhibits a low interfacial resistance of ∼16 Ω cm2 and an ultrastable long-term cycling behavior for 800 h under a current density of 200 μA/cm2, leading to Li//LiCoO2 solid-state batteries with good rate performance and cycling stability.

Phosphonitrile based porous organic polymers as effective flame-retardant electrolytes for lithium battery

Developing electrolytes with flame-retardant properties become the critical factor in making high safety lithium batteries. As phosphonitrile-based compounds are a kind of typical flame-retardant materials, herein, taking phosphonitrile-based aldehyde as the basic organic building blocks, two porous organic polymers (POPs) named as PVPH and PVPH-CO2H were successfully fabricated after solvothermal reaction with 1,3-diaminobenzene (MPD) and 5-carboxy-1,3-diaminobenzene (MPD-CO2H), respectively for electrolytes of lithium batteries. Studies revealed that both of the phosphonitrile-based POPs demonstrate good thermal stability and excellent flame-retardant properties, suggesting they are promising flame-retardant electrolytes for the application in battery. Battery performance investigations revealed that both of them, especially PVPH-CO2H, show good performance after assembling them into lithium batteries. This study paves the way to improve battery safety performance by employing the flame-retardant phosphonitrile-based porous polymers as effective electrolytes. Moreover, it also broadens the application of flame-retardant materials in energy storage materials.

Interface engineering enabling non-corrosive sulfonimide salt for 4.4 V class lithium batteries

Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) with outstanding electrochemical and thermal stability has promising applications in electrolytes for lithium batteries. However, a low concentration of the sulfonimide salt electrolyte can corrode a commonly used aluminum (Al) current collector, posing a perennial conundrum that hinders its wide application. In this work, we find that pure H2O as an additive in the 1 M LiTFSI electrolyte effectively protects the Al current collector from corrosion by TFSI−. The interface engineering by specific adsorption of H2O plays a pivotal role in regulating the structure of the electrical double layer on the Al foil surface, blocking the interaction of TFSI− with Al. Meanwhile, hydrogen bonds are verified between H2O and TFSI−, weakening the attack of TFSI− on the Al collector and improving the Li+ conductivity. The mechanism has been confirmed by theoretical calculations and a variety of characterizations. Benefiting from the addition of H2O, the lithium batteries exhibit excellent cycling performance at a high cut-off voltage of 4.4 V even at −20 °C and a 3 Ah pouch full cell shows long cycling performance. The results demonstrate the high compatibility of the H2O-added electrolyte with high voltage cathode, lithium metal and graphite anodes. This work introduces a strategy for the utilization of sulfonimide salt at high voltage and wide temperature even at a low concentration.