Organic Liquid Electrolytes Research Articles

(Invited) Different Designs for Ta-Doped Llzo Based Solid State Battery Prepared By Tape-Casting

One pathway for moving forward from current Li-ion battery technology based on organic liquid electrolytes to next-generation battery design can be implementation of solid state electrolyte along with Li metal based negative electrode. This step would result in a battery with higher energy density and improved safety.One promising candidate material for ceramic electrolyte is garnet-type oxide LLZO (Li7La3Zr2O12) due to its relatively good chemical stability which allows relaxed requirements for processing and handling. Additionally, the doped LLZO has sufficiently good Li+ ionic conductivity (0.1 – 1 mS/cm at room temperature) and exhibits (electro-)chemical stability with the electrode materials currently under focus. To achieve low resistance values, the LLZO electrolyte needs to be prepared as a thin layer with high density. In order to integrate fabrication of LLZO electrolyte into industrial manufacturing, tape-casting can be considered as one of the low-cost scalable method for producing ceramic layers.In this study tape-casting was used to produce Ta-doped LLZO electrolyte layers with relative density of 98% and total conductivity of 0.3 mS/cm at room temperature. In order to obtain Li/LLZO/Li symmetrical cells, interfacial treatment was used for surface of LLZO to achieve good contact and low interfacial resistance with Li metal electrode. Current densities up to 300 µA/cm2 were achieved during galvanostatic cycling for flat LLZO pellet sample at 40 °C. The cell was galvanostatically cycled with high stability for long term at current density of 100 µA/cm2.Another design that can be considered for LLZO-based solid state battery is porous-dense-porous multilayers. This architecture has the advantage to provide support for electrolyte layer allowing to reduce its thickness and also increases the interfacial surface area which will reduce interfacial resistance. The described design allows to obtain lower resistance for the solid state battery with higher accessible current densities (>1mA/cm2), thus providing higher performance.

Designing electrolytesand interphases for high-energy lithium batteries.

High-energy and stable lithium-ion batteries are desired for next-generation electric devices and vehicles. To achieve their development, the formation of stable interfaces on high-capacity anodes and high-voltage cathodes is crucial. However, such interphases in certain commercialized Li-ion batteries are not stable. Due to internal stresses during operation, cracks are formed in the interphase and electrodes; the presence of such cracks allows for the formation of Li dendrites and new interphases, resulting in a decay of the energy capacity. In this Review, we highlight electrolyte design strategies to form LiF-rich interphases in different battery systems. In aqueous electrolytes, the hydrophobic LiF can extend the electrochemical stability window of aqueous electrolytes. In organic liquid electrolytes, the highly lithiophobic LiF can suppress Li dendrite formation and growth. Electrolyte design aimed at forming LiF-rich interphases has substantially advanced high-energy aqueous and non-aqueous Li-ion batteries. The electrolyte and interphase design principles discussed here are also applicable to solid-state batteries, as a strategy to achieve long cycle life under low stack pressure, as well as to construct other metal batteries.

Dual Interface Compatibility Enabled via Composite Solid Electrolyte with High Transference Number for Long-Life All-Solid-State Lithium Metal Batteries.

The development of solid-state electrolytes (SSEs) effectively solves the safety problem derived from dendrite growth and volume change of lithium during cycling. In the meantime, the SSEs possess non-flammability compared to conventional organic liquid electrolytes. Replacing liquid electrolytes with SSEs to assemble all-solid-state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising energy storage/conversion technology for the future. Herein, a composite solid electrolyte containing two inorganic components (Li6.25Al0.25La3Zr2O12, Al2O3) and an organic polyvinylidene difluoride matrix is designed rationally. X-ray photoelectron spectroscopy and density functional theory calculation results demonstrate the synergistic effect among the components, which results in enhanced ionic conductivity, high lithium-ion transference number, extended electrochemical window, and outstanding dual interface compatibility. As a result, Li||Li symmetric battery maintains a stable cycle for over 2500h. Moreover, all-solid-state lithium metal battery assembled with LiNi0.6Co0.2Mn0.2O2 cathode delivers a high discharge capacity of 168mAhg-1 after 360 cycles at 0.1C at 25°C, and all-solid-state lithium-sulfur battery also exhibits a high initial discharge capacity of 912mAhg-1 at 0.1C. This work demonstrates a long-life flexible composite solid electrolyte with excellent interface compatibility, providing an innovative way for the rational construction of next-generation high-energy-density ASSLMBs.

Recent Research Progress on All-Solid-State Mg Batteries

Current Li battery technology employs graphite anode and flammable organic liquid electrolytes. Thus, the current Li battery is always facing the problems of low energy density and safety. Additionally, the sustainable supply of Li due to the scarce abundance of Li sources is another problem. An all-solid-state Mg battery is expected to solve the problems owing to non-flammable solid-state electrolytes, high capacity/safety of divalent Mg metal anode and high abundance of Mg sources; therefore, solid-state electrolytes and all-solid-state Mg batteries have been researched intensively last two decades. However, the realization of all-solid-state Mg batteries is still far off. In this article, we review the recent research progress on all-solid-state Mg batteries so that researchers can pursue recent research trends of an all-solid-state Mg battery. At first, the solid-state electrolyte research is described briefly in the categories of inorganic, organic and inorganic/organic composite electrolytes. After that, the recent research progress of all-solid-state Mg batteries is summarized and analyzed. To help readers, we tabulate electrode materials, experimental conditions and performances of an all-solid-state Mg battery so that the readers can find the necessary information at a glance. In the last, challenges to realize the all-solid-state Mg batteries are visited.

Micro-Sized MoS6@15%Li7P3S11 Composite Enables Stable All-Solid-State Battery with High Capacity

All-solid-state lithium batteries without any liquid organic electrolytes can realize high energy density while eliminating flammability issues. Active materials with high specific capacity and favorable interfacial contact within the cathode layer are crucial to the realization of good electrochemical performance. Herein, we report a high-capacity polysulfide cathode material, MoS6@15%Li7P3S11, with a particle size of 1–4 μm. The MoS6 exhibited an impressive initial specific capacity of 913.9 mAh g−1 at 0.1 A g−1. When coupled with the Li7P3S11 electrolyte coating layer, the resultant MoS6@15%Li7P3S11 composite showed improved interfacial contact and an optimized ionic diffusivity range from 10−12–10−11 cm2 s−1 to 10−11–10−10 cm2 s−1. The Li/Li6PS5Cl/MoS6@15%Li7P3S11 all-solid-state lithium battery delivered ultra-high initial and reversible specific capacities of 1083.8 mAh g−1 and 851.5 mAh g−1, respectively, at a current density of 0.1 A g−1 within 1.0–3.0 V. Even under 1 A g−1, the battery maintained a reversible specific capacity of 400 mAh g−1 after 1000 cycles. This work outlines a promising cathode material with intimate interfacial contact and superior ionic transport kinetics within the cathode layer as well as high specific capacity for use in all-solid-state lithium batteries.

Efficient Molecular Dynamics Simulations of Deep Eutectic Solvents with First-Principles Accuracy Using Machine Learning Interatomic Potentials.

In recent years, deep eutectic solvents emerged as highly tunable and ecofriendly alternatives to common organic solvents and liquid electrolytes. In the present work, the ability of machine learning (ML) interatomic potentials for molecular dynamics (MD) simulations of these liquids is explored, showcasing a trained neural network potential for a 1:2 ratio mixture of choline chloride and urea (reline). Using the ML potentials trained on density functional theory data, MD simulations for large systems of thousands of atoms and nanosecond-long time scales are feasible at a fraction of the computational cost of the target first-principles simulations. The obtained structural and dynamical properties of reline from MD simulations using our machine learning models are in good agreement with the first-principles MD simulations and experimental results. Running a single MD simulation is highlighted as a general shortcoming of typical first-principles studies if the dynamic properties are investigated. Furthermore, velocity cross-correlation functions are employed to study the collective dynamics of the molecular components in reline.

A stable and efficient quasi-solid-state photo/betavoltaic-powered electrochemical cell based on 3-dimensional CdS/ZnO heterostructure

Electrochemical betavoltaic (EBV) cells are promising power sources for low-power electronics in remote and harsh environments. However, their practical applications are limited by the organic liquid electrolytes with the inferior temperature stability and narrow electrochemical window. In this work, a quasi-solid-state EBV cell was fabricated using a high-conductive gel-based quasi-solid-electrolyte (QSE), a CdS-modificated ZnO nanorod arrays (ZNRAs) structure as the anode material, a radioactive 63Ni sheet as the cathode as well as the irradiation source. Monte Carlo (MC) simulations are utilized to determine the optimized length (2.97 μm) of the ZNRAs filled by electrolyte, Electrochemical photovoltaic (EPV) cells were used to assess and optimize the content of CdS loaded on the ZNRAs. The optimum EBV cell demonstrated an excellent long-term stability and a high energy-conversion efficiency of 10.09 % with a short-circuit current density of 0.755 μA cm−2 and an open-circuit voltage of 0.288 V. The porous CdS@ZNRAs core–shell structure filled by soft ionic liquids (IL)/gel-based QSE enables a large specific area of electrochemical interface network. The synergistic effects of 3-D CdS/ZnO heterostructure with type-II band alignment and IL/gel-based QSE are responsible for the enhanced ECE and improved long-term stability of EBV/EPV cells.

High ionic conductivity and critical current density of Li7−xLa2.95Yb0.05Zr2−xTaxO12 solid electrolyte by modulation of Li+ distribution

Safety concerns caused by organic liquid electrolyte in lithium battery might limit its application. Li7La3Zr2O12 is a promising electrolyte for solid-state lithium batteries due to its high ionic conductivity and interfacial stability with lithium. The influence of Ta doping on the structure, transport property and ionic conductivity of Li7−xLa2.95Yb0.05Zr2−xTaxO12 (0 ≤ x ≤ 0.2) has been investigated. Ta drives some Li ions from 24d to 96 h site and simultaneously optimizes the size of Li ion transport pathway. This structure modification increases the mobility, jump rate, and diffusion coefficient of lithium ion. Besides, the densification and grain contact have also been enhanced. The ionic conductivity of Li6.85La2.95Yb0.05Zr1.85Ta0.15O12 reaches 1.07 × 10−3 S cm−1 at 30 °C. The solid-state battery assembled with Li6.85La2.95Yb0.05Zr1.85Ta0.15O12 exhibits high critical current density of 1.1 mA cm−2 and discharge capacity of 166.7 mAh g−1, indicating that Li6.85La2.95Yb0.05Zr1.85Ta0.15O12 is a competitive solid electrolyte for solid-state lithium batteries.

Stabilizing Decavanadate Cluster as Electrode Material in Sodium and Lithium-ion Batteries.

Decavanadate ([V10 O28 ]6- , {V10 }) clusters are a potential electrode material for lithium and post-lithium batteries; however, their low stability due to the solubility in liquid organic electrolytes has been challenging. These molecular clusters are also prone to transform into solid-state oxides at a moderate temperature needed in the typical electrode fabrication process. Hence, controlling the solubility and improving the thermal stability of compounds are essential to make them more viable options for use as battery electrodes. This study shows a crystal engineering approach to stabilize the cluster with organic guanidinium (Gdm+ ) cation through the hydrogen-bonding interactions between the amino groups of the cation and the anion. The comparison of solubility and thermal stability of the Gdm{V10 } with another cluster bearing tetrabutylammonium (Tba+ ) cation reveals the better stability of cation-anion assembly in the former than the latter. As a result, the Gdm{V10 } delivers better rate capability and cycling stability than Tba{V10 } when tested as anode material in a half-cell configuration of a sodium-ion battery. Finally, the performance of the Gdm{V10 } anode is also investigated in a lithium-ion battery full cell with LiFePO4 cathode.

In-situ polymerized gel polymer electrolytes for stable solid-state lithium batteries with long-cycle life

The practical application of high energy density lithium batteries is significantly limited by serious safety concerns and chemical instability of traditional organic liquid electrolytes. In this work, polyethylene glycol (PEG) based gel polymer electrolyte (GPE) supported by polyethylene (PE) separator is proposed by in-situ polymerization. The obtained GPE with 50% liquid electrolyte (LE) exhibits an ionic conductivity of 2.22 × 10−4 S cm−1 at 30 °C, a wide electrochemical stability window up to 4.7 V and high lithium ion transference number of 0.502. Furthermore, the GPE displays good interfacial compatibility with lithium anode and the Li//Li symmetric battery with PE supported GPE can cycle stably for 2800 h. In addition, the LiFePO4//Li solid state batteries show outstanding charging/discharging performances at both 30 °C and 60 °C. Particularly, the battery can stable cycle over 1000 cycles at 1 C under 30 °C with capacity retention of 83.36%; meanwhile, it shows a high initial reversible capacity of 149.8 mAh g−1 with excellent cycling stability over 200 cycles at 1 C under 60 °C. This work provides an in-situ polymerized GPE and its promising potential application in lithium metal batteries with a long-cycle life.

Single‐Ion Conducting Polymer Electrolyte for Superior Sodium‐Metal Batteries

AbstractSodium‐metal batteries (SMBs) are considered a potential alternative to high‐energy lithium‐metal batteries (LMBs). However, the high reactivity of metallic sodium towards common liquid organic electrolytes renders such battery technology particularly challenging. Herein, we propose a multi‐block single‐ion conducting polymer electrolyte (SIPE) doped with ethylene carbonate as suitable electrolyte system for SMBs. This novel SIPE provides a very high ionic conductivity (2.6 mS cm−1) and an electrochemical stability window of about 4.1 V at 40 °C, enabling stable sodium stripping and plating and excellent rate capability of Na||Na3V2(PO4)3 cells up to 2 C. Remarkably, such cells provide a capacity retention of about 85 % after 1,000 cycles at 0.2 C thanks to the very high Coulombic efficiency (99.9 %), resulting from an excellent interfacial stability towards sodium metal and the Na3V2(PO4)3 cathode.

Single-Ion Conducting Polymer Electrolyte for Superior Sodium-Metal Batteries.

Sodium-metal batteries (SMBs) are considered a potential alternative to high-energy lithium-metal batteries (LMBs). However, the high reactivity of metallic sodium towards common liquid organic electrolytes renders such battery technology particularly challenging. Herein, we propose a multi-block single-ion conducting polymer electrolyte (SIPE) doped with ethylene carbonate as suitable electrolyte system for SMBs. This novel SIPE provides a very high ionic conductivity (2.6 mS cm-1) and an electrochemical stability window of about 4.1 V at 40 °C, enabling stable sodium stripping and plating and excellent rate capability of Na||Na3V2(PO4)3 cells up to 2C. Remarkably, such cells provide a capacity retention of about 85% after 1,000 cycles at 0.2C thanks to the very high Coulombic efficiency (99.9%), resulting from an excellent interfacial stability towards sodium metal and the Na3V2(PO4)3 cathode.

Research progress of organic liquid electrolyte for sodium ion battery.

Electrochemical energy storage technology has attracted widespread attention due to its low cost and high energy efficiency in recent years. Among the electrochemical energy storage technologies, sodium ion batteries have been widely focused due to the advantages of abundant sodium resources, low price and similar properties to lithium. In the basic structure of sodium ion battery, the electrolyte determines the electrochemical window and electrochemical performance of the battery, controls the properties of the electrode/electrolyte interface, and affects the safety of sodium ion batteries. Organic liquid electrolytes are widely used because of their low viscosity, high dielectric constant, and compatibility with common cathodes and anodes. However, there are problems such as low oxidation potential, high flammability and safety hazards. Therefore, the development of novel, low-cost, high-performance organic liquid electrolytes is essential for the commercial application of sodium ion batteries. In this paper, the basic requirements and main classifications of organic liquid electrolytes for sodium ion batteries have been introduced. The current research status of organic liquid electrolytes for sodium ion batteries has been highlighted, including compatibility with various types of electrodes and electrochemical properties such as multiplicative performance and cycling performance of electrode materials in electrolytes. The composition, formation mechanism and regulation strategies of interfacial films have been explained. Finally, the development trends of sodium ion battery electrolytes in terms of compatibility with materials, safety and stable interfacial film formation are pointed out in the future.

Probing the Formation of Cathode-Electrolyte Interphase on Lithium Iron Phosphate Cathodes via Operando Mechanical Measurements.

Interfacial instabilities in electrodes control the performance and lifetime of Li-ion batteries. While the formation of the solid-electrolyte interphase (SEI) on anodes has received much attention, there is still a lack of understanding the formation of the cathode-electrolyte interphase (CEI) on the cathodes. To fill this gap, we report on dynamic deformations on LiFePO4 cathodes during charge/discharge by utilizing operando digital image correlation, impedance spectroscopy, and cryo X-ray photoelectron spectroscopy. LiFePO4 cathodes were cycled in either LiPF6, LiClO4, or LiTFSI-containing organic liquid electrolytes. Beyond the first cycle, Li-ion intercalation results in a nearly linear correlation between electrochemical strains and the state of (dis)-charge, regardless of the electrolyte chemistry. However, during the first charge in the LiPF6-containing electrolyte, there is a distinct irreversible positive strain evolution at the onset of anodic current rise as well as current decay at around 4.0 V. Impedance studies show an increase in surface resistance in the same potential window, suggesting the formation of CEI layers on the cathode. The chemistry of the CEI layer was characterized by X-ray photoelectron spectroscopy. LiF is detected in the CEI layer starting as early as 3.4 V and LixPOyFz appeared at voltages higher than 4.0 V during the first charge. Our approach offers insights into the formation mechanism of CEI layers on the cathode electrodes, which is crucial for the development of robust cathodes and electrolyte chemistries for higher-performance batteries.

A Novel Approach for Development of Stable Quasi‐Solid Lithium‐O2 Batteries: Assembly and Performances of Double Layer Gel Polymer Electrolytes

AbstractGel‐polymer electrolytes (GPEs) offer a suitable alternative to flammable organic liquid electrolytes in lithium‐oxygen batteries (LOBs) to address safety concerns. However, a major challenge with GPEs is their low ionic conductivity. To enhance the ionic conductivity of GPEs, active inorganic particles have been incorporated. To increase the ionic conductivity of GPE, active inorganic particles have been reinforced in GPE. While this increases the ionic conductivity, it also leads to blockage of the cathode porous structure and reduces the actual surface area of the cathode materials, resulting in poor battery performance. This study proposes a novel double‐layer polymer gel electrolyte (d‐GPE) that exhibits both high ionic conductivity and stability for quasi solid‐state LOBs. The double‐layer GPE consists of a bare GPE layer integrated in the cathode, and a composite GPE (c‐GPE, containing 5 wt. % lithium aluminum titanium phosphate (LATP)), which is in contact with Li anode and bare‐GPE. The produced double‐layer gel polymer electrolyte displays high reaction kinetic and better stability due to the excellent electrode/electrolyte interface and rapid oxygen diffusion in the air‐cathode. Furthermore, the d‐GPE electrolyte is resistant to fire and protects Li from dendrite growth and water molecules attack, indicating tremendous promise for the development of practical LOBs.

Operando Hard X-Ray Photoelectron Spectroscopy for Observing Interfacial Electrochemical Reactions in All-Solid-State Batteries

All-solid-state lithium-ion batteries (ASS-LIBs) have been attracting wide attention for their potential superior performance, such as high safety and long cycle life compared with the conventional lithium-ion batteries with liquid organic electrolytes. However, one of the critical problems of the ASS-LIBs for wide spread applications, especially for electric vehicles, is the large interfacial resistance across the electrode/solid electrolyte (SE)1. When an electrode and SE come into contact, some mobile ions are redistributed at the interface according to their potential difference2,3. In addition, the distribution of the mobile ions and electric potential are also changed during the battery operations. Therefore, dynamic observation of their distribution across the electrode/SE interface is essential to identify and control the origin of the interfacial resistance.Hard x-ray photoelectron spectroscopy (HAXPES) is capable of nondestructive analysis of the elemental composition, oxidation states and electronic structure of sample surfaces and interfaces including those buried with over layers at depth > 10 nm[4].In this study, we developed a laboratory-based operando HAXPES system equipped with a Cr-Kα source (5414.9 eV), which enables angle-resolved measurements of and bias applications to the sample transferred without air-exposure, and applied it to the charging/discharging reactions of a LiCoO2 (LCO) positive electrode deposited on a Li6.6La3Zr1.6Ta0.4O12 (LLZT) solid electrolyte in a half cell configuration. HAXPES measurements were performed while the LCO electrode was electrically grounded to a hemispherical analyzer.The galvanostatic charge/discharge potential profiles exhibited a characteristic plateau due to delithiation of a O3-LiCoO2 at ~3.9 V vs. Li+/Li5. In the Co 2p 3/2 region of the pristine cell, a sharp intense main peak and a broad satellite peak typical to a LCO were observed. At the charged states, however, the main peak was asymmetrically broadened to the higher binding energy. The main peak was deconvoluted into two peaks at 780 eV and ~781 eV, corresponding to Co3+ ions and Co4+ ions, respectively. The full width half maximums (FWHMs) of the Co4+ ions peak increased at charged states, while that of the Co3+ ions peak was remained unchanged. Furthermore, the relative areas of satellite peak decreased at the charged states. These results suggest that Co3+ ions were oxidized to the Co4+ ions by delithiation of the LCO electrode6,7. After the subsequent discharging, the component of higher binding energy of the main peaks decreased, and the satellite peak increased. In addition, the FWHMs of the Co4+ ions peak decreased, suggesting that the Co4+ ions were reduced by lithiation into the LCO electrode during discharging. Thus, the lithiation/delithiation of LCO was successfully observed by operando HAXPES.References N. Ohta, K. Takada, L. Zhang, R. Ma, M. Osada and T. Sasaki, Advanced Materials, 18, 2226 (2006) K. Yamamoto, Y. Iriyama, T. Asaka, T. Hirayama, H. Fujita, C. A. Fisher, K. Nonaka, Y. Sugita and Z. Ogumi, Angew Chem Int Ed Engl, 49, 4414 (2010) J. Haruyama, K. Sodeyama, L. Han, K. Takada and Y. Tateyama, Chemistry of Materials, 26, 4248 (2014) N. K. F. Curran Kalha, Prajna Bhatt, et al., Journal of Physics: Condensed Matter, 33, 233001 (2021) J. N. Reimers and J. R. Dahn, The Electrochemical Society, 139, 2091 (1992) L. Dahéron, R. Dedryvère, H. Martinez, M. Ménétrier, C. Denage, C. Delmas and D. Gonbeau, Chemistry of Materials (2008) H. Kiuchi, K. Hikima, K. Shimizu, R. Kanno, F. Toshiharu and E. Matsubara, Electrochemistry Communications, 118, 106790 (2020)

Cathode Development for All Solid-State Lithium-Sulfur Batteries

With higher demand for alternative energy sources that are cleaner and more sustainable, research has shifted towards various lithium metal-based batteries with higher capacities than lithium-ion (LIBS). The study of lithium-sulfur energy storage systems has been heavily influenced due to the high gravimetric capacity of sulfur (1672 mA h g−1) and its abundance in the Earth’s crust. To increase the safety of lithium-sulfur batteries, solid state systems have been developed. These systems are also advantageous as the polysulfide shuttle effect normally seen in organic liquid electrolytes (OLEs) is eliminated, decreasing degradation due the irreversible reactions. Some of the most successful electrolytes found for lithium-sulfur all solid-state batteries (ASSLSBs) are ceramic based electrolytes. These electrolytes have high ionic conductivities (ranging 10-3-10-4 S cm-1) and do not pose any safety risks. However, one of the biggest bottlenecks of ASSLSBs is the utilization and accessibility of sulfur during cycling.To ensure these attributes are met, carbon materials have been used as supports; additionally, carbon also aids in electron transport due sulfur’s low electrical conductivity (10 -15 S m-1).Sulfur is typically dispersed or deposited on these carbon supports in different approaches before a full cathode composition is developed. Varying synthesis methods of sulfur deposition onto reduced graphene oxide are studied to determine which synthesis method provides the most accessibility for sulfur utilization. Utilization and accessibility will be analyzed through cyclic voltammetry, galvanostatic charge and discharge and impedance measurements to obtain characteristic voltammograms, specific capacity curves and Nyquist plots. Cells are assembled in PEEK Split cells using ceramic based electrolyte and lithium metal for the development of a noble ASSLSB.

Lithium Dendrite Growth Suppression in Anode-Free Lithium Battery Using Bifunctional Electrospun Gel Polymer Electrolyte Membrane

Anode free Li metal battery (AFLMB) are being intensively investigating in recent years as a means to achieve higher capacity when compared with standard Li metal batteries. However, the severe electrolyte decomposition during plating/stripping cycles, that causes fast Li dendrite growth and quick capacity fading, is challenging for its commercialization. Herein, poly (vinylidene fluoride-hexafluoropropylene) polymer containing Li1.6Al0.4Mg0.1Ge1.5(PO4)3 ceramic filler (90:10 w% ratio, PVDF-HFP-10) gel polymer electrolyte (GPE) is employed for the first time in AFLMB to suppress the Li dendrite growth and homogeneous Li deposition is achieved during Li metal plating/stripping. The PVDF-HFP-10 based membrane is manufactured using electrospinning technique, which is well known and effective technique to increase the amount of crystalline β-phase of PVDF-HFP, on Cu collector foil. Particularly, a pure crystalline β-phase of PVDF-HFP has been observed in the adhesion layer sticked with Cu collector as confirmed from the analysis of Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy measurements. The adhesion layer is further investigated using X-ray absorption spectroscopy (XAS), grazing angle X-ray diffraction (GAXRD) and X-ray photoelectron spectroscopy (XPS) techniques. The GAXRD analysis reveals Cu collector undergoes slight reconstruction of its (100) facets surface to (200) facets in the presence of the adhesion layer. Moreover, depth XPS analysis confirmed that the alignment of F atoms in the adhesion layer is toward the Cu collector which can play an important role for homogeneous Li deposition. Based on these findings, a novel approach is developed to prepare GPE, without peeling off the electrospun PVDF-HFP membrane from Cu collector to take advantage of the adhesion layer. The electrospun PVDF-HFP membrane GPE unpeeled off from its Cu collector (Cu@PVDF-HFP-10) prepared using novel method provides bifunctional applications, as electrolyte and as an artificial solid-electrolyte interphase (ASEI). The strong electrostatic interaction between the fiber sheet and its collector foil forms an adhesion layer (⁓0.5μm) which acts as ASEI prevents electrolyte decomposition. The Cu@PVDF-HFP-10|Li anode free cell enables uniform and highly compacted Li platting, excellent electrochemical performance, and high coulombic efficiency (CE) even at a high current density up to 5 mA cm− 2 (CE, 97.14%) after 200 cycles using 2 mAh cm− 2 capacity loading. Conversely, nonuniform and thick Li deposition is observed in the GPE prepared by conventional method (PVDF-HFP-10), due to poor contact between the membrane and the electrode, achieved only 90.08% CE after 100 cycles at 5 mA cm− 2. Post-cycling analyses using titration-gas chromatography (TGC) and XPS techniques indicated that the new strategy is conducive to prevent dead Li metal formation as well as to create a carbonate-free, robust, and stable SEI convenient to develop sustainable AFLMB system. Cycling performance of the Cu@PVDF-HFP-10 GPE utilized in the Cu|NMC AFLMB configuration delivered much better electrochemical performance than the PVDF-HFP-10 GPE (prepared by traditional method) and organic liquid electrolytes.

Flash Point of Gel-Polymer Electrolytes: Effect of the Molecular Interaction between Nitrile (HNBR) and Carbonyl (PC)

Gel-polymer electrolytes are receiving increasing attention as they compromise between a good ionic conductivity (10-3S/cm) [1, 2] and good safety features. The solvent trapped into the polymeric matrix increases the ionic conductivity while the polymeric matrix enhances safety due to its mechanical strength repressing dendrite growth [3, 4]. Gel polymer electrolytes are almost universally presumed to be less flammable than current commercialize battery (organic liquid electrolyte) [5, 6]. However, there is no universal test to compare the flammability of a liquid and the flammability of a gel.Our work focuses on the flash point measurement of gel-polymer electrolytes. The flash point temperature is a standardized test and is one of the top experiments to measure flammability [7]. The Flash point temperature is well studied for liquid electrolytes [7, 8] but had never been conducted for gel-polymers. We developed a method to analyze the flash point of gel-polymer electrolytes by pairing the closed-cup flash point tester with a thermal imaging camera. This new apparatus was used it to analyze a promising system: HNBR with different grade of nitrile doped with PC. The goal is to find the relation between the flash point and the nitrile contains in the polymeric matrices.Our research sheds light on the effect of molecular interactions between the nitrile of HNBR and the carbonyl of PC on the flammability of the overall gel-polymer electrolyte with FT-IR. The study has also been conducted adding a lithium salt (LiTFSI) to be representative of real battery application. Agrawal, R.C. and G.P. Pandey, Solid polymer electrolytes: materials designing and all-solid-state battery applications: an overview. J. Phys. D: Appl. Phys., 2008. 41(22): p. 223001-223019.Cheng, X., et al., Gel Polymer Electrolytes for Electrochemical Energy Storage. Advanced Energy Materials, 2018. 8(7).Hassouna, J. and B. Scrosati, Review—Advances in Anode and Electrolyte Materials for the Progress of Lithium-Ion and beyond Lithium-Ion Batteries. Journal of The Electrochemical Society, 2015. 162 p. A2582-A2588.Ren, W., et al., Advanced gel polymer electrolytes for safe and durable lithium metal batteries: Challenges, strategies, and perspectives. Energy Storage Materials, 2021. 34: p. 515-535.Castillo, J., et al., Safe, Flexible, and High-Performing Gel-Polymer Electrolyte for Rechargeable Lithium Metal Batteries. Chemistry of Materials, 2021. 33(22): p. 8812-8821.Li, Q., et al., Progress in electrolytes for rechargeable Li-based batteries and beyond. Green Energy & Environment, 2016. 1(1): p. 18-42.Liu, X.S. and Z.Y. Liu, Research Progress on Flash Point Prediction. Journal of Chemical and Engineering Data, 2010. 55(9): p. 2943-2950.Catoire, L., S. Paulmier, and V. Naudet, Experimental determination and estimation of closed cup flash points of mixtures of flammable solvents. Process Safety Progress, 2006. 25(1): p. 33-39.

Bulk SEI: Investigating the Instability of Li6PS5Cl at the Lithium Metal Anode

Among the multitude of lithium ion conducting materials, thiophosphate-based solid electrolytes (thio-SEs) attract great attention from academia and industry alike. Due to their high ionic conductivities and increased safety, thio-SEs – such as lithium argyrodite Li6PS5Cl – are considered suitable to be employed in solid-state batteries (SSBs). Thus, by substituting liquid organic electrolytes of lithium-ion batteries (LIBs), higher energy and power densities (in combination with lithium metal anodes (LMAs)) as well as simplified cell designs are promoted.[1] Unfortunately, one major drawback of thio-SEs is the inadequate reduction stability in contact with LMAs,[2] which impedes device-level applications and has to be overcome.Due to its thermodynamic instability, Li6PS5Cl is reduced upon contact with highly reactive lithium metal to a mixture of compounds, i.e., Li2S, Li3P, and LiCl. Thus, a so-called solid electrolyte interphase (SEI) is formed, which is predominantly ion-conducting. Its electronically insulating nature is suspected to limit the interphase formation and further growth.[3] Additionally, the chemical and structural properties differ from that of pure SE. Unfortunately, the SEI only evolves at the Li | Li6PS5Cl interface and its thickness is in the nanometer range.[4] Suitable methods to examine the characteristics of SEI layers are therefore scarce and mostly limited to surface sensitive characterization techniques.Here, we employ a novel approach to gain further insights into the nature of SEI layers of thiophosphate-based SE in contact with lithium metal, demonstrated with Li6PS5Cl as model solid electrolyte. Bulk material corresponding to the composition of the SEI is synthesized from SE and Li-metal in a direct manner and hence, examined in respect to different properties. The successful synthesis of bulk-phase SEI is confirmed by X-ray photoelectron spectroscopy measurements, validating the chemical composition. This is complemented by structural analysis. Electrochemical characterization (electrochemical impedance spectroscopy and Wagner-Hebb) is utilized to quantify the ionic and electronic conductivity of the obtained bulk material, respectively, and to further determine transport properties and SEI growth at the Li | Li6PS5Cl interface. The combined results of our studies allow comprehensive understanding of the SEI nature and offer boundary conditions to approximate the nanoscale properties of the SEI at the Li | Li6PS5Cl interface from bulk material synthesis and analysis.