Conventional Liquid Electrolytes Research Articles

Charge–Discharge Performance of Positive Electrodes for Fluoride-Shuttle Batteries Using Fluorohydrogenate Ionic Liquid Electrolytes

1. Introduction Fluoride-shuttle batteries (FSBs) are attracting increasing attention because they possess superior energy densities compared to conventional lithium-ion batteries. In the past decade, fluoride-ion conducting solid electrolytes have been widely studied for FSBs [1,2]. However, most of them require operating temperature higher than 373 K. To decrease the operating temperature, ether-based organic solvents and ionic liquids were recently applied to FSBs [3–5]. We have focused on fluorohydrogenate ionic liquids (FHILs) for FSBs because FHILs exhibit ionic conductivities much higher than conventional liquid electrolytes. For example, [C2C1im][(FH)2.3F] (C2C1im = 1-ethyl-3-methylimidazolium) shows an ionic conductivity as high as 100 mS cm−1 at room temperature (298 K) [6,7]. We have already reported charge–discharge behaviors of CuF2 electrodes in this IL [8]. In the present study, charge–discharge behaviors of copper-based positive electrodes were further investigated in several FHILs at room temperature. 2. Experimental All experiments were conducted at room temperature (ca. 298 K). Three-electrode cells were used for electrochemical measurements. The working electrode was composed of the active material (CuF2 or metallic copper), acetylene black as a conductive agent, and polytetrafluoroethylene as a binder. Both the counter and reference electrodes were CuF2/Cu electrodes. Two FHILs, [C2C1im][(FH)2.3F] and [C2C1pyrr][(FH)2.3F] (C2C1pyrr = N-ethyl-N-methylpyrrolidinium), were used as electrolytes. Cyclic voltammetry was performed at 10 mV s−1 before charge–discharge tests. The working electrodes after the tests were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). Prior to these analyses, the electrolytes were removed by washing with dehydrated ethanol, and the samples were transferred to all the analytical instruments without air exposure. The solubility of CuF2 was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The solution for the ICP-AES measurement was prepared by immersion and stirring of excess CuF2 particles in each FHIL for 1 day. 3. Results and Discussion Fig. 1 shows charge–discharge curves of a metallic copper electrode in [C2C1im][(FH)2.3F] electrolyte at a rate of 0.05C (= 42.2 mA (g-Cu)−1). The initial charge and discharge capacities are 439 and 599 mAh (g-Cu)−1, respectively. The results of XRD and XPS analyses suggested the reversible reactions during charge–discharge cycling.Cu + 6[(FH)2F]− ⇌ CuF2 + 4[(FH)3F]− + 2e− (1)The discharge capacity larger than the charge capacity in the initial cycle may be attributed to the presence of oxide film on the surface of copper particles. The discharge capacity rapidly decreases after the 2nd cycle, and reaches 167 mAh (g-Cu)−1 at the 20th cycle, which corresponds to the capacity retention ratio of 28%. The SEM observation indicates that this steep decline in reversible capacities is likely ascribed to aggregation of active materials.Concerning [C2C1pyrr][(FH)2.3F] electrolyte, the same charge–discharge test was performed at 0.05C rate. Fig. 2 summarizes the cycling properties of discharge capacities in the two electrolytes. Initial discharge capacity obtained in [C2C1pyrr][(FH)2.3F] is 400 mAh (g-Cu)−1, which is lower than that in [C2C1im][(FH)2.3F]. However, the discharge capacity is 210 mAh (g-Cu)−1 at the 20th cycle, exhibiting the improved capacity retention of 53%. This improved cycleability is probably originated from the lower solubility of CuF2 formed in the charging reaction. According to the ICP-AES results, the solubilities of CuF2 were ca. 100 and 20 ppm for [C2C1im][(FH)2.3F] and [C2C1pyrr][(FH)2.3F], respectively. Due to the higher solubility in [C2C1im][(FH)2.3F], the dissolution and reprecipitation of CuF2 occur more severely on the surface of the working electrode, leading to more intense aggregation of the active material. The utilization of [C2C1pyrr][(FH)2.3F] mitigates such degradation of the electrode. Acknowledgments This study is based on results obtained from a project, "Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING2)", JPNP16001, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Building Block Design for Rapid Mass Transport in Quasi-Solid-State Solar Cells

Mesoscopic solar cells have rapidly emerged as a promising alternative to conventional silicon photovoltaics due to the combined benefits of low-cost, simple fabrication and competitive solar energy conversion efficiency. Recent success in low light absorption cobalt (II/III) polypyridyl complexes has led to encouraging solar energy conversion efficiencies in excess of 13%. Moreover, as one-electron redox mediators, cobalt (II/III) complexes based DSC systems also show a lower overpotential for dye regeneration and better compatibility with flexible metal substrates than iodide/tri-iodide. Such efforts open up great possibilities towards commercial applications.In contrast to the conventional organic liquid electrolytes that commonly have challenges durable encapsulation of the devices due to solvent evaporation, gel electrolytes have exhibited an impressive long-term stability, especially for outdoor applications where temperature of the DSC system can reach 80-85 oC under sunlight. Improvement on mass transport of the considerably large sized cobalt (II/III) complexes, particularly in high viscosity electrolyte, is crucial for solid-state dye-sensitized solar cells (SS-DSCs) to reach a reliable high efficiency toward practical applications.In this work, titania nanorod aggregates (TNA) with a great specific surface area and well-developed crystalline network were synthesized through a solvothermal approach and utilized as photoanode building blocks for application in cobalt (II/III) tris(2′2-bipyridine) complexes based solid-state electrolyte. An initial efficiency excess 7.1% and a long term stable efficiency of approximately 8.0% were achieved at full sun illumination by freshly assembled and aged TNA SS-DSCs, respectively. This represents dramatic enhancements of nearly 35% and 100% against the SS-DSCs prepared from two standard TiO2 nanoparticle samples – CCIC (approx. 5.9%) and Degussa P25 (approx. 4.0%), correspondingly. The TNA is characterised by a combination of mesopores within each aggregate and macro inter-aggregates voids, a high specific surface area and a great light scattering ability; such features make the aggregates superior photoanode building blocks for the application in bulky cobalt redox mediator based SS-DSCs system.

Composite Electrolyte Composed of Li1.5Al0.5Ti1.5(PO4)3 and PVDF-Based Gel Electrolyte Containing Highly Concentrated Electrolytes

Li ion conducting inorganic solid electrolytes have been widely investigated because of their high thermal stability and single-ion conducting property. Recently, some of inorganic solid electrolytes were found to have high ionic conductivity in the order of 10-3−10-2 S/cm at room temperature, which are comparable to that of conventional liquid electrolytes. The use of a Li metal anode, which has a high specific capacity, can significantly increase the cell energy density. However, most of the inorganic solid electrolytes are known to be thermodynamically unstable against Li metal and form the decomposition phases, which cause high interfacial resistance between electrode | electrolyte and degrade the cell performance. Surface roughness and brittleness of inorganic solid materials, which make the poor interfacial contact, are known to cause the increase in the interfacial resistance between electrode and electrolyte. To address these issues, much effort has been devoted to developing composite electrolytes combining inorganic solid electrolytes with polymer electrolytes. Poly(ethylene oxide) (PEO) is often used in fabricating composite electrolytes because of its advantageous characteristics such as processability, flexibility and Li ion solvation ability. However, there are intrinsic problems such as low Li transference number of ~0.2, low ionic conductivity in the order of 10-5 mS/cm at room temperature, and poor oxidative stability. Polymer gel electrolytes composed of ionic liquids and polymer network are self-standing and flexible while inheriting the properties of ionic liquids such as high ionic conductivity, electrochemical stability, and nonflammability.In the present study, we prepared a flexible composite electrolyte by combining a NASICON type Li1.5Al0.5Ti1.5(PO4)3 (LATP) fillers and a polymer gel electrolyte. The gel electrolyte was composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and a liquid electrolyte of LiN(SO2CF3)2 (LiTFSA)/sulfolane (SL). The molar ratio of [LiTFSA]/[SL] was controlled to be 1/2. The gel electrolyte (without LATP) was prepared by a solution casting method, and the obtained gel was flexible. The electrochemical properties of the gel electrolyte are comparable to that of the liquid electrolyte of [LiTFSA]/[SL] = 1/2, which has a relatively high transference number of ~0.64. The composite electrolytes composed of the gel and LATP mixed in various ratios were prepared. The solid-state 6Li magic-angle spinning (MAS) NMR measurements revealed that the Li ion exchange reaction occurred at the interface between LATP and the gel electrolyte, suggesting that both LATP and gel phases contribute to the Li ion conduction in the composite electrolytes. However, AC impedance measurement for the interface between LATP and gel electrolyte suggested that the resistance for the Li-ion transfer at the interface causes the increase in resistance of the composite electrolyte, resulting in the decrease in ionic conductivity. We will present the effects of the LATP/gel electrolyte interface on the physicochemical properties of the composite electrolyte such as ionic conductivity and Li-ion transference number. We will report the charge-discharge performance of lithium batteries using the composite electrolytes.

Fast Determination of the Limiting Ionic Diffusion Coefficient in Lithium Metal Polymer Batteries

The energy conversion and its storage is a tremendous challenge for our society. Despite the great progress of the Lithium (Li)-ion technology based on flammable liquid electrolyte, their intrinsic instability is a strong safety issue for large-scale applications. The use of solid polymer electrolytes (SPEs) is an adequate solution in terms of safety and energy density thanks to their stability towards Li metal.[1] Moreover, as for conventional liquid electrolyte, the cationic transference number of poly(ethylene oxide) based SPE is typically below 0.2 which limits their power performance due to the formation of concentration gradient throughout the electrodes.[2] In such Li metal battery, the SPE acts as both separator and functionalized cathode binder ensuring ionic transport all over the battery. To increase the battery energy density a simple way is to use thicker cathode. Indeed, for a given electrode formulation, the energy density is directly linked to the active material loading.[3]The goal of this study is to propose a quick and efficient methodology to optimize the thickness of the SPE and of the cathode based on charge transport parameters, which allows to determine the effective limiting Li+ diffusion coefficient. Revisiting a protocol by Doyle et al.[4] the battery power performance is rapidly established, at least 8 time faster than conventional cycling (charge-discharge steps) with a similar accuracy as depicted in Figure 1.[5] Then, by using an approach based on the Sand equation a limiting current density is determined. A unique mother curve of the capacity as a function of the limiting current density is obtained whatever the electrode and electrolyte thicknesses. Finally, the effective limiting diffusion coefficient is estimated which in turn allows to design the best electrode depending on electrolyte thickness.

Continuum Description of the Role of Negative Transference Numbers on Ion Motion in Polymer Electrolytes

All-solid-state rechargeable batteries are considered to be the key solution for the development of next-generation electrical energy storage. Solid polymer electrolytes (SPEs) have gained attention due to their electrochemical stability, non-flammability and processability.[1, 2] It is widely recognized that the ionic conductivity of polymer electrolytes is significantly lower than that of conventional liquid electrolytes. Recent studies have shown that salt diffusivity as well as cation transference number in polymer electrolytes is also lower than conventional electrolytes. [3-7] In fact, the cation transference number is negative in a narrow but important salt concentration window and it coincides with the peak in conductivity with respect to salt concentration. At a fundamental level, knowledge of these transport parameters can be used to characterize ion motion in SPEs. This knowledge is essential for predicting battery performance and may serve as a foundation for designing polymers with better performance.Recently, the experimental and theoretical approaches have been performed to better understand the transport of each ionic species. New experimental techniques such as electrophoretic NMR (eNMR) are emerging as powerful methods for directly measuring ion velocities in electrolytes under applied electric fields. [8-10] The standard approach to interpret these experiments is built on the assumption that electrolyte is dilute and thermodynamically ideal.[11] Timachova et al.[11] derived modified expressions for interpreting the eNMR data using concentrated solution theory. These expressions only apply at very early times after polarization when concentration gradients and diffusive fluxes can be neglected. However, they shed no light on the time- and space-dependence of the velocities of the cations and anions.The aim of this study is to provide a deeper understanding of the transient behavior of cations and anions in polymer electrolytes. We examine the role of diffusion and migration in a poly(ethylene oxide)-based (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) electrolytes using concentrated solution theory. This formulation was used to investigate how these negative transference numbers influence the magnitudes and directions of ion velocities when a fixed current is imposed on the electrolyte during the passage of current. Under the constraint of electroneutrality, this study reveals the interplay between diffusion and migration by thorough examination of the local velocity, salt concentration gradient, and flux of ions within the solution. Examining the differences in ion motion when the transference number is negative and comparing it to cases when it is positive, allows us to demonstrate the dynamic nature of the system during galvanostatic conditions. The study also reveals conditions where experimental methods need to focus in order to detect unexpected species migration under negative transference conditions.[1] M. Armand, Solid State Ionics, 9-10 (1983) 745-754.[2] A.K. Shukla, T.P. Kumar, Curr Sci India, 94 (2008) 314-331.[3] R. Bouchet, S. Maria, R. Meziane, A. Aboulaich, L. Lienafa, J.P. Bonnet, T.N.T. Phan, D. Bertin, D. Gigmes, D. Devaux, R. Denoyel, M. Armand, Nat Mater, 12 (2013) 452-457.[4] C.Y. Tang, K. Hackenberg, Q. Fu, P.M. Ajayan, H. Ardebili, Nano Lett, 12 (2012) 1152-1156.[5] J.W. Park, K. Yoshida, N. Tachikawa, K. Dokko, M. Watanabe, J Power Sources, 196 (2011) 2264-2268.[6] Y.P. Ma, M. Doyle, T.F. Fuller, M.M. Doeff, L.C. Dejonghe, J. Newman, J Electrochem Soc, 142 (1995) 1859-1868.[7] D.M. Pesko, Z.G. Feng, S. Sawhney, J. Newman, V. Srinivasan, N.P. Balsara, J Electrochem Soc, 165 (2018) A3186-A3194.[8] Z.Y. Zhang, L.A. Madsen, J Chem Phys, 140 (2014).[9] M. Gouverneur, F. Schmidt, M. Schonhoff, Phys Chem Chem Phys, 20 (2018) 7470-7478.[10] M.P. Rosenwinkel, M. Schonhoff, J Electrochem Soc, 166 (2019) A1977-A1983.[11] K. Timachova, J. Newman, N.P. Balsara, J Electrochem Soc, 166 (2019) A264-A267.

X-Ray Microtomography Analysis of Li-Sulfur Batteries with a Block Copolymer Electrolyte

Li-ion batteries are the dominant solution for many applications, from small electronic devices up to hybrid and fully electric vehicles.[1] However, this technology is now mature and new chemistries are needed to reach high specific energy while ensuring safety. Despite a relatively low operating voltage, sulfur (S8) is an attractive cathode active material due to its high theoretical specific capacity; a factor of six higher than traditional LiCoO2 cathodes.[2] To realize high energy density systems, the S8 cathode must be paired with a Li metal anode. Many challenges remain to be addressed to effectively couple a Li metal with a S8 cathode such as the low S8 utilization, the strong volume change of active material upon cycling, the insulating nature of S8 and of the final product Li2S, the solubility of polysulfides in the electrolyte.[3] This issues lead to poor capacity retention, limited cycle life, and low Coulombic efficiency. To address the polysulfide dissolution problem one approach consists in confining S8 within mesoporous and nanoporous carbon.[4] However, conventional liquid electrolytes are not stable against Li metal. A solution is then to use a solid polymer electrolytes, such as polystyrene-b-poly(ethylene oxide) (SEO) block copolymer doped with LiTFSI salt, known to stabilize Li metal.[5]The goal of this study is to understand the behavior of Li-S8 batteries comprising a SEO electrolyte. The cathode is a composite made of carbon, SEO electrolyte and sulfur-impregnated carbon nanospheres.[6] The cells were cycled and exhibited significant capacity fade. We thus used hard X-ray microtomography to determine the reason for this capacity fade. Figure 1 represents tomography images prior and after cycling. In addition to polysulfide dissolution, our observations indicate that the battery failure in our system is also due to strong changes at the Li/SEO interface.

Asymmetric Polymer Electrolyte Constructed by Metal–Organic Framework for Solid‐State, Dendrite‐Free Lithium Metal Battery

AbstractSolid‐state polymer electrolytes (SPEs) with flexibility, easy processability, and low cost have been regarded as promising alternatives for conventional liquid electrolytes in next‐generation high‐safety lithium metal batteries. However, SPEs generally suffer poor strength to block Li dendrite growth during the charge/discharge process, which severely limits their wide practical applications. Here, a rational design of 3D cross‐linked network asymmetric SPE modified with a metal–organic framework (MOF) layer on one side is proposed and prepared through an in‐situ polymerization process. In such unique asymmetric SPEs, the nanoscale MOF layer acts as a shield that effectively suppresses the growth of Li dendrites and regulates the uniform Li+ transport, and the polymer electrolyte can be scattered in the whole cell to endow the smooth transmission of Li+. As a result, the asymmetric SPE exhibits high ionic conductivity, wide electrochemical window, high thermal stability and safety, which endows the Li/Li symmetrical cell with outstanding cyclic stability (operate well over 800 h at a current density of 0.1 mA cm−2 for the capacity of 0.1 mAh cm−2).

Optimized ion-conductive pathway in UV-cured solid polymer electrolytes for all-solid lithium/sodium ion batteries

Solid electrolyte-based lithium-ion batteries (LIBs) have enormous potential to replace conventional LIBs with flammable liquid electrolytes. However, most solid electrolytes show low ionic conductivity and poor interfacial properties with electrodes, preventing them from reaching the level of conventional liquid electrolyte systems with separators. Herein, we optimized the formation of an ion-conductive pathway in a UV-cured solid polymer electrolyte (USPE) via a semi-interpenetrating polymer network with a minimal liquid content. The USPE consists of a UV-curable hard matrix (trimethylolpropane ethoxylate triacrylate, ETPTA) as a backbone film with negligible ionic conductivity and an optimized ionic channel with an ion-solvated gel polymer (Li+/PVdF-HFP) with a minimal liquid content for boosting the Li+ conduction. The hybrid solid-state film provides high ionic conductivity (up to 85%) relative to commercial liquid electrolyte systems and a stable electrochemical window. We also applied the same USPE with Na+ for solid electrolyte-based sodium ion batteries, and similar positive effects were also observed. Going another step forward, both the PVdF-HFP/ETPTA ratio and the HFP content in the PVdF-HFP are critical gel polymer additives for generating reinforced Li+ ion pathways in USPE.

On-site-coagulation gel polymer electrolytes with a high dielectric constant for lithium-ion batteries

This paper reports a gel polymer electrolyte (GPE) that is synthesized as a liquid solution and transforms into a gel on-site after injection into lithium-ion batteries (LIBs). The GPE is produced by mixing poly (acrylonitrile-co-methacrylate) (P(AN-co-MA)) and polyethylene glycol (PEG) with a conventional carbonate-solvated LiPF6 liquid electrolyte (LE). P(AN-co-MA) dissociates counter-ion pairs and PEG promotes polymer-crosslinking for electrolyte gelation. The GPE has a high dielectric constant and low dielectric loss because of ion-pair dissociation and facilitated ion motion. When incorporated with a separator, the GPE exhibits an ionic conductivity of 1.7 × 10−3 S cm−1 and a Li transference number (tLi+) of 0.62. The corresponding values for the LE are 9.1 × 10−4 S cm−1 and 0.37, respectively. The high dielectric permittivity and tLi+ render the GPE stable at 5.2 V (vs. Li/Li+). The GPE outperforms the LE when assembled into Li||LiFePO4 batteries, exhibiting superior capacity, high rate retention, and cycling stability. Moreover, the GPE has low flammability such that a graphite|GPE|LiFePO4 pouch-cell battery operates smoothly under folding or after truncation. The on-site coagulation design ensures that the developed GPE can be used in existing LIB assembly lines to produce high-quality LIBs that can be applied in diverse power devices.

Mitigating Interfacial Instability in Polymer Electrolyte-Based Solid-State Lithium Metal Batteries with 4 V Cathodes

Solid polymer electrolytes (SPEs) are attractive for next-generation energy storage, since they are more thermally stable compared to conventional liquid electrolytes and simpler for scalable manufacturing than ceramic electrolytes. However, there is a growing body of research suggesting that the interfacial instabilities between SPEs and other battery components (e.g. electrodes and electrolyte fillers) hinder their practical applications. This perspective highlights the degradation mechanisms at these interfaces revealed by recent works, especially in lithium/4 V cathode systems with high energy density. We also review recent progresses on mitigating such instabilities, and provide perspectives on how to further understand and address these issues, such as advanced characterizations and simulations, which delivers a valuable guide for future studies to accelerate the development of SPEs-based solid-state batteries.

Postinjection gelation of an electrolyte with high storage permittivity and low loss permittivity for electrochemical capacitors

The use of gel polymer electrolytes (GPEs) in electric double layer capacitors (EDLCs) is limited by the liquid injection assembly line currently used in EDLC manufacturing. This paper proposes a postinjection gelated GPE, which can be synthesized by mixing a polymer blend of poly(acrylonitrile-co-methyl acrylate) and poly(ethylene glycol) (i.e., PANMA:EG) with a conventional liquid electrolyte (LE). The as-synthesized GPE is in liquid state and can be applied in the liquid injection assembly line. The gelation time can be tuned by varying the composition of the polymer blend. The functionalities on the polymer chains facilitate the dissociation of ion pairs and suppress the formation of ion–solvent complexes; thus, the GPE has an ionic conductivity that is three times that of the LE. Under polarization for dielectric analysis, the GPE exhibits high storage permittivity and low loss permittivity because of its swift ion motion and polymeric dipole orientation. Owing to its superior permittivity performance, the resulting GPE-EDLC outperforms the LE-EDLC in terms of the ultimate capacitance, rate capability, and charge–discharge cycling stability. The postinjection gelation feature and outstanding permittivity characteristics indicate the suitability of this GPE in industrial-scale assembly lines and practical applications.

Novel Sodium–Poly(tartaric acid)Borate-Based Single-Ion Conducting Polymer Electrolyte for Sodium–Metal Batteries

The limitations of conventional organic liquid electrolytes such as sodium dendrite growth, serious side reactions, and liquid leakage hinder the development of sodium–metal batteries (SMBs). In th...

Crosslinked solidified gel electrolytes via in-situ polymerization featuring high ionic conductivity and stable lithium deposition for long-term durability lithium battery

A high-power lithium battery exhibits nearly 100% capacity retention after 150 cycles at 4C/4C charge/discharge is achieved by solidified gel electrolytes (SGEs) with remarkably high ionic conductivity of 9 mS cm−1 at room temperature. A series of SGEs is comprised by poly(ethylene oxide) (PEO) polymer precursor with conventional liquid electrolyte with superior lithium dendrite growth suppression that enables long-cycle life and high-power lithium batteries. The battery also improves safety with minimal gas generation at 100 °C. Solid-like property increases as the crosslinked density enhances the gelation property of the SGEs. The less crosslinked SGE preserves the great battery capacity similar to the liquid electrolyte of 64 mAh g − 1 at 10 C rate. Furthermore, highly crosslinked SGE exhibits nearly 100% capacity retention after 150 cycles with charge/discharge rate of 4C/4C that surpassed the liquid electrolyte. SEM image shows that the SGE form a uniform passivation layer on the lithium metal surface that provide good cycling durability. By simply controlling the crosslinked density with the length of crosslinker, desired battery performance can be achieved. Consequently, these findings accelerate the practical application for the solidified gel electrolytes with superior safety and durability in lithium battery.

Fire-Preventing LiPF6 and Ethylene Carbonate-Based Organic Liquid Electrolyte System for Safer and Outperforming Lithium-Ion Batteries.

Battery safety is an ever-increasing significance to guarantee consumer's safety. Reducing or preventing the risk of battery fire and explosion is a must for battery manufacturers. Major reason for the occurrence of fire in commercial lithium-ion batteries is the flammability of conventional organic liquid electrolyte, which is typically composed of 1 M LiPF6 salt and ethylene carbonate (EC)-based organic solvents. Herein, we report the designed 1 M LiPF6 and EC-based nonflammable electrolyte including methyl(2,2,2-trifluoroethyl)carbonate, which breaks the conventional perception that EC-based liquid electrolyte is always flammable. The designed electrolyte also provides high anodic stability beyond the conventional charge cut-off voltage of 4.2 V. A graphite∥LiNi0.6Co0.2Mn0.2O2 lithium-ion full cell with our designed EC-based nonflammable electrolyte with a small fraction of vinylene carbonate additive under an aggressive condition of 4.5 V charge cut-off voltage, 0.5C rate, and 45 °C exhibits increased capacity, reduced interfacial resistance, and improved performance and rate capability. A basic understanding of how a high-voltage cathode-electrolyte interface and anode-electrolyte interface are stabilized and how failure modes are mitigated by fire-preventing electrolyte is discussed.

Implementation of Bismuth Chalcogenides as an Efficient Anode: A Journey from Conventional Liquid Electrolyte to an All-Solid-State Li-Ion Battery.

Bismuth chalcogenide (Bi2X3; X = sulfur (S), selenium (Se), and tellurium (Te)) materials are considered as promising materials for diverse applications due to their unique properties. Their narrow bandgap, good thermal conductivity, and environmental friendliness make them suitable candidates for thermoelectric applications, photodetector, sensors along with a wide array of energy storage applications. More specifically, their unique layered structure allows them to intercalate Li+ ions and further provide conducting channels for transport. This property makes these suitable anodes for Li-ion batteries. However, low conductivity and high-volume expansion cause the poor electrochemical cyclability, thus creating a bottleneck to the implementation of these for practical use. Tremendous endeavors have been devoted towards the enhancement of cyclability of these materials, including nanostructuring and the incorporation of a carbon framework matrix to immobilize the nanostructures to prevent agglomeration. Apart from all these techniques to improve the anode properties of Bi2X3 materials, a step towards all-solid-state lithium-ion batteries using Bi2X3-based anodes has also been proven as a key approach for next-generation batteries. This review article highlights the main issues and recent advances associated with Bi2X3 anodes using both solid and liquid electrolytes.

Development of polymer electrolyte membranes based on biodegradable polymer

Over the use of conventional liquid electrolytes, polymer based electrolytes have paid a special attention in the area of energy research mainly because of their flexibility and ease of availability. From the last few decades, non-degradable and synthetic polymers had been used as host polymers for the development of highly ionic conducting polymer electrolytes. From our earlier studies, different polymer electrolytes based on synthetic polymer such as polyethylene oxide (PEO) have also been studied with obtained conductivity values of the order of 10−7-10−4 S/cm. Three orders of increase in conductivity has been observed with the addition of additives such as plasticizer as well as nano filler and some of the data is represented in this paper. But in the present scenario, use of biodegradable polymer electrolytes is highly preferable over non-degradable polymer electrolytes because of their renewability and biocompatibility. Also, the use of blend and additives in the polymer electrolytes have become the most promising ways to improve the ion transport as well as electrochemical performance of polymer electrolytes. Polymer electrolytes based on specially the biodegradable polymer have been addressed to bring one step ahead to show the enhanced ionic conductivity, mechanical stability and improved interfacial stability towards electrode materials. Present paper highlights a review on the recent research efforts dedicated by researchers to understand the ion conduction mechanism in the modified polymer electrolytes as well as the usefulness of the biodegradable Polycaprolactone (PCL) as a host polymer in different polymer electrolytes.

Facile fabrication of solution-processed solid-electrolytes for high-energy-density all-solid-state-batteries by enhanced interfacial contact

Instead of commercial lithium-ion batteries (LIBs) using organic liquid electrolytes, all-solid-state lithium-ion batteries (ASSBs) employing solid electrolytes (SEs) are promising for applications in high-energy–density power applications and electric vehicles due to their potential for improving safety and achieving high capacity. Although remarkable progress in SEs has been achieved and has resulted in high ionic conductivity, which now reaches values comparable to those of liquid electrolytes, the typical use of a slurry process for the fabrication of conventional ASSBs inevitably causes harmful reactions between sulfide materials and polar solvents. Here, we studied the efficient infiltration process of SE slurry into conventional composite LIB electrodes (NCM622) for achieving high-energy-density ASSBs via a scalable solution-based fabrication process. Two methods are proposed to ensure that SE materials are evenly distributed and sufficiently infiltrated into the porous structures of LIB electrodes. The LPSCl SE solutions were effectively infiltrated into the electrodes at higher processing temperatures and the temperature was subsequently optimized at above the boiling point of the ethanol solvent due to the dynamic motion of SE molecules via a convective flow during solvent vaporization. Moreover, the porous LIB composite electrodes with a mixture of active materials of different particle sizes formed and filled capillary pores resulting in a high electrode density. The LPSCl SE-infiltrated NCM622 electrodes that used this strategy could remarkably improve the initial discharge capacity of ASSBs to as high as 177 mAh/g. These ASSBs also showed excellent performance even at high loading values (about 17 mg/cm2), making them competitive with LIBs using conventional liquid electrolytes.

The effect of lithium salt type on ionic conductivity of poly(vinylidene difluoride)-based solid polymer electrolytes

Recently, research on solid polymer electrolytes (SPEs) for lithium-ion batteries (LIBs) has been actively carried out as an alternative to conventional liquid electrolytes that present safety issues such as flammability and explosion. However, the SPEs show relatively low ion conductivity, compared to the liquid electrolytes. In this study, a poly(vinylidene difluoride) (PVDF)-based SPE was prepared by introducing two different electrolytes; one is weak-binding lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt mixture with solvating plastic crystal succinonitrile (SN) and the other is lithium bis(fluorosulfonyl)imide (LiFSI) salts. Among the SPEs studied, the PVDF/LiFSI-containing SPE membrane exhibited the highest room temperature ion conductivity of 1 x 10−3 S/cm, characterized by electrochemical impedance spectroscopy (EIS).

Application of a Holed Cathode and Anode Prepared with a Picosecond Pulsed Laser for Lithium Ion Batteries (1)~ Performance of Holed Cathodes with Solid-State Electrolytes~

The design of the interface between the electrode and electrolyte is very important and should be carefully considered during the development of lithium-ion batteries (LIBs) with a high rate performance; this is especially true for all-solid-state LIBs. Recently, we developed a structure with holes fabricated with a picosecond pulsed laser and showed an improvement in the rate performance of a holed cathode in liquid electrolyte-based LIBs. In this study, a holed structure was applied to solid-state electrolytes (SSEs), such as Li1+x+yAlxTi2-xSiyP3-yO12 (LATP) and poly(ethylene oxide)(PEO)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The filling of SSE particles instead of a conventional liquid electrolyte into the holes on the cathode produced a high rate performance, indicating that the advantage of a holed structure could be applied to all-solid-state LIBs.

Simultaneously enhancing the thermal stability and electrochemical performance of solid polymer electrolytes by incorporating rod-like Zn2(OH)BO3 particles

Solid polymer electrolytes provide high safety and good electrochemical stability in solid-state lithium batteries (SSLBs) compared with conventional liquid electrolytes. In this work, a novel solid polymer composite electrolyte based on poly (ethylene oxide) (PEO) filled with rod-like Zn2(OH)BO3 particles was prepared by a grinding process followed with a heating treatment process and a cold pressing process. The effect of the incorporation amount of rod-like Zn2(OH)BO3 particles on the ionic conductivity was investigated systemically. It is found that 10 mol% of rod-like Zn2(OH)BO3 particles addition resulted in a highest ionic conductivity of 2.78 × 10−5 at 30 °C and the improved ionic conductivity was considered to be caused by the reducing of PEO crystallinity and the increasing of Li ion migrating pathway on the interface between the Zn2(OH)BO3 and PEO. In addition, the optimum composite electrolyte exhibited a high electrochemical stability window of 4.51 V (vs. Li/Li+), good lithium stability and excellent thermal stability.