Carbonate-based Liquid Electrolyte Research Articles

Pectin alignment induced changes in ion solvation structure in ethylene carbonate-based liquid electrolytes

Classical molecular dynamics simulations are used to explore the impact of the alignment of pectin over the randomized configuration on ion solvation structure in pectin-loaded ethylene carbonate - lithium bis(trifluoromethanesulfonyl) imide electrolytes. Our study focuses on how biological macromolecules, specifically pectin, influence the behavior of liquid electrolytes, considering their applications in rechargeable batteries due to their ion solvation capabilities and ion transport characteristics. Aligned pectin causes a tightly packed first coordination shell of anions around lithium ions by weakening the long-ranged interactions beyond the first coordination shell compared to a random configuration. Consequently, the number of pectin oxygens around lithium decreases dramatically from 3 to 2, resulting in an overall diluted solvation shell containing fewer numbers of anions and pectin oxygens around lithium ions. With polymer alignment, the non-Gaussianity increases from 3.387 to 6.550 for lithium ions and from 0.475 to 0.621 for TFSI ions, reflecting a 90% increase in dynamic heterogeneity for lithium ions and a 30% increase for TFSI ions. Cation-cation correlations enhance ionic conductivity in randomized pectin, whereas isolated anion motion dominates in aligned pectin due to cation-pectin interactions. Our work not only highlights potential strategies for improving electrolyte performance in rechargeable batteries but also emphasizes the crucial role of molecular orientation in optimizing electrolyte properties, paving the way for more optimized and efficient battery technologies.

Influence of LiNO3 on the Lithium Metal Deposition Behavior in Carbonate-Based Liquid Electrolytes and on the Electrochemical Performance in Zero-Excess Lithium Metal Batteries.

Continuous lithium (Li) depletion shadows the increase in energy density and safety properties promised by zero-excess lithium metal batteries (ZELMBs). Guiding the Li deposits toward more homogeneous and denser lithium morphology results in improved electrochemical performance. Herein, a lithium nitrate (LiNO3 ) enriched separator that improves the morphology of the Li deposits and facilitates the formation of an inorganic-rich solid-electrolyte interphase (SEI) resulting in an extended cycle life in Li||Li-cells as well as an increase of the Coulombic efficiency in Cu||Li-cells is reported. Using a LiNi0.6 Co0.2 Mn0.2 O2 positive electrode in NCM622||Cu-cells, a carbonate-based electrolyte, and a LiNO3 enriched separator, an extension of the cycle life by more than 50 cycles with a moderate capacity fading compared to the unmodified separator is obtained. The relative constant level of LiNO3 in the electrolyte, maintained by the LiNO3 enriched separator throughout the cycling process stems at the origin of the improved performance. Ion chromatography measurements carried out at different cycles support the proposed mechanism of a slow and constant release of LiNO3 from the separator. The results indicate that the strategy of using a LiNO3 enriched separator instead of LiNO3 as a sacrificial electrolyte additive can improve the performance of ZELMBs further by maintaining a compact and thus stable SEI layer on Li deposits.

Interfacial Challenge for Solid-State Lithium Batteries- Liquid Addition

All solid-state lithium batteries with garnet electrolytes (Li7La3Zr2O12, LLZO) are promising energy storage devices that have gained increasing attention due to their huge potential towards non-flammability and higher energy density. However, reported solid-state lithium batteries cannot achieve the projected energy density (> 500 Wh/kg at the cell level) mainly due to insufficient contact and poor compatibility between LLZO and electrodes. The use of liquid electrolytes in small quantities has been suggested as a component in the quasi-solid hybrid electrolytes to address these two issues. However, the working principle of liquid electrolytes added as the interface inside the batteries is not clear yet.This study added 10L carbonate-based liquid electrolyte between LLZO and LiNi0.6Mn0.6Co0.2O2 (NMC 622) cathode. The assembled Li|LLZO|NMC 622 cell exhibited an initial discharge capacity of 168 mAh g-1 with a capacity retention ratio of ~82 % after 28 cycles. Scanning Transmission X-ray Microscopy revealed the reaction of LE with garnet and NMC 622. More importantly, the LE decomposed and solidified during the cycling process. Decomposed LE participated in the formation of a newly-identified solid-liquid electrolyte interface (SLEI) just after the 1st cycle. Furthermore, the X-ray Absorption Spectroscopy results indicated that the SLEI consisted predominantly of LiF, LaF3, Li2O, and Li2CO3 species.Overall, this study proved the solidification of liquid electrolytes at the garnet/cathode interface. The formation of SLEI effectively suppressed the degradation of the garnet electrolyte and stabilized the battery cycling performance. More efforts are required to optimize the liquid and establish a more stable SLEI that could expand the cycling life of the batteries.

Partially Neutralized Polyacrylic Acid as an Efficient Binder for Aqueous Ceramic-Coated Separators for Lithium-Ion Batteries.

A partially neutralized polyacrylic acid (Pn-PAA) is used for coating sub-micron-sized α-alumina on a conventional microporous polyolefin separator, fabricating a ceramic-coated separator (CCS). Pn-PAA acts as a dispersant and binder by adsorbing itself on alpha(α)-alumina surfaces under acidic condition through the columbic interaction, providing a repulsive force to disperse fine alumina in aqueous suspension, and binds alumina strongly on plasma-treated separator through hydrogen bonding. This CCS shows favorable wettability in carbonate-based liquid electrolyte and ionic conduction due to the high hydrophilicity of Pn-PAA and alumina. With that, this study found that Pn-PAA-made-CCS yields a substantial adhesion strength of ~106 N/m with enhanced cycle stability, a specific capacity of 145.0 mAh/g after 200 cycles at 1 C at room temperature in half cells (LFP/Li metal).

Zeolite membrane separators for fire-safe Li-ion batteries – Effects of crystal shape and membrane pore structure

The state-of-the-art lithium-ion batteries (LIB) use carbonate-based liquid electrolytes and polymeric separators which pose safety issues including fire-hazard. The use of fire-retarding salt-concentrated electrolytes can address the safety issues of LIBs, but these electrolytes have high viscosity and low wettability with polymeric separators making it difficult to fabricate high performance LIBs with the electrolytes. Here we report development of zeolite membrane separators with tailored pore structure and surface chemistry for preparation of fire-safe LIBs using salt-concentrated electrolytes. The zeolite membrane separators are made of zeolite particles with a specific zeolite structure, Si/Al ratio, and different particle shapes, coated on cathode by a scalable blade coating method. Intermediate pore, pure silica MFI-type zeolite (silicalite) was selected as the fire-proof material for membrane separators which also offer high wettability for the fire-retarding salt-concentrated electrolyte of lithium bis(fluorosulfonyl)imide (LiFSI) in tri-methyl phosphate solvent (TMP) solvent. Two silicalite membrane separators of similar pore size but different porosity and tortuosity were coated on cathode (LiNi0.5Mn0.3Co0.2O2 or NMC) using plate-shaped silicalite particles of low aspect ratio (LAR) and high aspect ratio (HAR). Both zeolite separators show significantly better wettability for the LiFSI/TMP electrolyte than the commercial polypropylene (PP) separator allowing fabrication of high-performance NMC/LiFSI-TMP/graphite cells with the non-combustible silicalite separator. The new fire-safe zeolite-membrane-based LIBs with the fire-retarding electrolyte exhibit excellent charge and discharge characteristics and cycle performance (similar to the state-of-the-art, but fire-unsafe LIBs with LiPF6-carbonate electrolyte and polymer separator). The membrane separators made of HAR plate-shaped zeolite showing low interparticle porosity and high tortuosity perform better than the membrane made of LAR zeolite particles, due to a more uniform lithium-ion flux from both interparticle pores and intraparticle zeolitic pores at the separator/anode interface.

Core-shell structure of polyacrylate-based binder enhancing the wet-adhesion strength and the kinetics of lithium-ion diffusion

Despite constituting only a small fraction of the mass of an electrode, the binder is one of the key components ensuring the long-term durability of lithium-ion batteries (LIBs). The need for higher energy density and superior power characteristics necessitates the enhancement of the adhesion properties of the binder to reduce the binder contents of electrodes. In this study, we synthesized a core-shell structured poly(acrylonitrile-co‑butyl acrylate) binder that exhibits higher adhesion strength, lower kinetic resistance, and higher electrode and cell lithium-ion diffusion coefficients than those of styrene-butadiene rubber, which is widely used in commercial LIBs. The polystyrene (PS) constituting the core enhanced the electrical conductivity, while the lone pairs of electrons of poly(acrylonitrile-co‑butyl acrylate) expedited the lithium ion movement, thereby enhancing the kinetics of LIBs. The adhesion properties were enhanced in the presence of the carbonate-based liquid electrolyte owing to the carboxyl groups introduced by itaconic acid on the shells.

Dynamic Anion Delocalization of Single-Ion Conducting Polymer Electrolyte for High-Performance of Solid-State Lithium Metal Batteries

Lithium metal batteries (LMBs) have been considered as next-generation energy storages due to their extremely high theoretical specific capacity (3860 mAh g-1). However, current LMBs, using conventional liquid electrolytes, still could not fulfill the demand of soaring expansion of energy era, such as electrical vehicles, because of their safety issues, originated by uncontrollable electrolytic side reaction on the lithium, resulting unstable solid-electrolyte interphase (SEI) and vicious lithium dendritic growth [1]. Also, carbonate-based liquid electrolytes have an intrinsic flammability, and the lithium dendrite, which short-circuits a cell, can lead to severe safety hazard with the unfavorable flammability of current liquid system when they are ignited. Therefore, solid-state electrolytes have been spotlighted recently for a pathway for safe, and high energy and power LMBs, due to their superior thermal stability and low vapor pressure, while maintaining suitable electrolytic performances.In this study, solid-state single-ion conducting polymer electrolytes (SICPEs), utilizing dynamic anion delocalization (DAD), realizing high ionic conductivity and dimensional stability for high-performance LMB, are studied. The SICPEs enable superior lithium transference number, resulting in highly reduced concentration gradient of lithium cation along the electrolyte to suppress the undesirable lithium dendritic growth. However, SICPEs have prominently lower ionic conductivity than dual-ion conducting polymer electrolyte (DICPEs), which is a critical issue to make a slower charge/discharge for SICPEs [2]. Although an approach utilizing gel polymer electrolyte (GPE), using a liquid solvent as a plasticizer, has been exploited to increase the ionic conductivity of SICPEs, GPEs have struggled with lower mechanical stability, compared to solid state, and still existing flammability issue with the plasticizer. The novel plasticizer, which is described here, can interact with bulky anionic polymer matrix, so that the negative charge can be dispersed onto the whole complex by DAD. Once the bulky complex is formed by DAD, the dissociation of lithium cation from anionic matrix can be easier with the decreased activation energy and higher ionic conduction. While increasing the ionic conductivity with DAD, the nature of polymeric plasticizer will highly suppress flammability. DAD allows the membrane endure more tensile strength due to the dynamic structural change in crosslinking state, so that the polymer electrolyte can tolerate dendritic growth of lithium by morphological change on an electrode surface.The obvious advantages of DAD-induced solid polymer electrolytes in this study for a high energy and power, and ultra-safe LMB can present a novel approach of polymer electrolyte design to the astronomical demand of energy storages.[1] F. Ahmed, I. Choi, M.M. Rahman, H. Jang, T. Ryu, S. Yoon, L. Jin, Y. Jin, W. Kim, ACS Appl. Mater. Interfaces 2019, 11, 34930-34938.[2] D.-M. Shin, J.E. Bachman, M.K. Taylor, J. Kamcev, J.G. Park, M.E. Ziebel, E. Velasquez, N.N. Jarenwattananon, G.K. Sethi, Y. Cui, J.R. Long, Adv. Mater. 2020, 32, 1905771.

Revealing the Role of Liquid Electrolytes in Cycling of Garnet-Based Solid-State Lithium-Metal Batteries

Solid-state lithium-metal batteries (SS-LMBs) suffer from the very high resistance at the garnet electrolyte/cathode interface that hampers their commercialization. Herein, a carbonate-based liquid electrolyte (LE) is introduced at the interface of a Li6.5La2.9Ba0.1Zr1.4Ta0.6O12 (LLBZTO) garnet/LiNi0.6Mn0.2Co0.2O2 (NMC 622) cathode to lower the interfacial resistance and improve the battery performance. In this work, we conducted a thorough study on the role of liquid electrolytes at the interface using scanning transmission X-ray microscopy (STXM) associated with X-ray absorption spectroscopy (XAS). As a result, we have shown new data related to the formation and the chemical composition of the two formed interphases: a solid–liquid electrolyte interphase (SLEI) and the cathode–electrolyte interphase (CEI). Furthermore, we have presented evidence that LE decomposes during cycling into fluoride species including LiF and LaF3, oxides like Li2O, and carbonates (i.e., Li2CO3) as the main components of in situ-formed SLEI. Based on the synergy between SLEI and CEI, we demonstrate Li|garnet|LE|NMC 622 cells cycled with an initial discharge capacity of 168 mAh g–1 and a capacity retention of ∼82% after 28 cycles. We expect that our study of SLEI will accelerate the implementation of a new hybrid electrolyte (solid garnet and liquid electrolyte) approach in SS-LMBs.

Poly(ethylene oxide)-Based Electrolytes for Solid-State Potassium Metal Batteries

Most conventional batteries today employ organic liquid electrolytes (LEs) that are not only flammable, but also serve as a medium for irreversible side reactions at the electrode interfaces, especially when metal is used as electrode. In post-lithium systems, such as potassium batteries, this issue is even more pronounced due to a higher reactivity of the metal as compared to lithium, and typically results in electrochemical instability leading to a rapid capacity fade of the battery.[1] When switching from LEs to solid polymer electrolytes (SPEs) that typically show better electrochemical stability at low (< 0.5 V vs. K+/K) and high (> 4 V vs. K+/K) potentials due to polymers inherent inertness, enhanced cycle life of the battery is expected.[2] Moreover, well-known disadvantage of SPEs in Li-based batteries, i.e., poor ionic conductivity at ambient temperature, could be overcome in systems with larger cation size, e.g. K+ [3,4], potentially removing some of the bottlenecks previously encountered in the case of Li-transport.In this presentation, a series of poly(ethylene oxide) - potassium bis(trifluoromethane sulfonyl)imide (PEO-KTFSI) compositions with different salt concentration was investigated for their potential application as SPEs in potassium metal batteries. To identify the most promising candidate in terms of ion transport and mechanical integrity, the effect of KTFSI concentration on thermal, rheological and electrochemical properties was studied. Several electrolyte compositions were examined in solid-state potassium batteries with a potassium metal negative electrode, and a positive electrode from Prussian blue analogue family. Our results reveal the advantages of solid-state systems with respect to improved capacity retention and Coulombic efficiency as compared to the reference system with carbonate-based LE, as demonstrated in Figure 1, thus paving the way for a new generation of potassium batteries with significantly improved key performance parameters. Figure 1. Comparison of potassium half-cells employing different electrolyte systems: carbonate-based liquid electrolyte (LE) vs. PEO-based solid polymer electrolyte (SPE) (a) capacity retention and (b) corresponding Coulombic efficiencies.[1] H. Wang, D. Zhai, F. Kang, Energy Environ. Sci. 2020, 13, 4583–4608.[2] J. Mindemark, M. J. Lacey, T. Bowden, D. Brandell, Prog. Polym. Sci. 2018, 81, 114–143.[3] M. Perrier, S. Besner, C. Paquette, A. Vallée, S. Lascaud, J. Prud’homme, Electrochim. Acta 1995, 40, 2123–2129.[4] U. Oteo, M. Martinez-Ibañez, I. Aldalur, E. Sanchez-Diez, J. Carrasco, M. Armand, H. Zhang, ChemElectroChem 2019, 6, 1019–1022. Figure 1

Understanding the Role of Liquid Electrolytes in Performance Improvement of Solid-State Lithium Metal Batteries

Garnet-type Li7La3Zr2O12 (LLZO) Solid-State Electrolytes (SSEs) enable Solid-State Lithium Metal Batteries (SSLMBs) with high power density due to their superior ionic conductivity over 1 mS cm-1 at room temperature and good chemical stability against Lithium (Li) metal. A major cause of failure in SSLMBs is the large interfacial resistance between LLZO and electrodes. The high resistance at the interfaces is normally associated with insufficient solid-solid surface contact. It is a common practice to introduce a Liquid Electrolyte (LE) in SSLMBs either in combination with SSEs to form quasi-solid electrolytes or as the interface to enhance battery cycling performance. Several studies are conducted on resolving the contact issue between LLZO and the Li-metal anode but very few focused on the LLZO/cathode interface.In this research, a carbonate-based LE was introduced at the interface of Li6.5La2.9Ba0.1Zr1.4Ta0.6O12 (LLBZTO) | LiNi0.6Mn0.6Co0.2O2 (NMC 622) cathode with the aim of understanding the mechanism which the LE enhances the SSLMBs performance, using the Scanning Transmission X-ray Microscopy (STXM) and X-ray Absorption Scanning (XAS). The assembled Li | LLBZTO SSEs | LE | NMC 622 cell exhibited an initial discharge capacity of 168 mAh g-1 with a capacity retention ratio of ~82 % after 30 cycles. The results from the STXM revealed the reactions of the LE with LLZO and NMC 622. The XAS analysis showed the formation of two new interfaces: Cathode-Electrolyte Interface (CEI) and Solid-Liquid Electrolyte Interface (SLEI). Also, the result indicated that the LE decomposed completely in the cell after 30 cycles and transformed to a dense and robust SLEI. This in turn led to the enhanced interfacial contact with the cathode and an improved Li+ ion transport at the interface. In addition, fluorides (i.e., LiF and LaF3) and carbonates (i.e., Li2CO3) were confirmed as the main components of the SLEI. In this study, two interfaces in SSLMBs (CEI and SLEI) were characterized. Fully understanding the roles of LE as the interface would enhance the practical application of quasi-solid electrolytes in SSLMBs. Keywords Solid-state lithium metal batteries; Garnet; Interface; Ceramic electrolyte; STXM

Cyclic Carbonate-Based, Single-Ion Conducting Polymer Electrolytes for Li-Ion Batteries: Electrolyte Design

Solid polymer electrolytes (SPEs) have been the focus of study to address Li-ion battery issues including thermal runaway by mitigating the danger from volatile solvents. A single ion conductor has a high transference number which eliminates uncontrolled mass transport by immobilizing the anion to the polymer matrix. Problems with undesired side reactions and lithium dendrite growth can also be improved by providing a mechanical barrier. Unfortunately, single-ion conducting SPEs suffer from poor lithium-ion mobility and conductivity due to the immobilized nature of the anions, poor ion-pair dissociation, and the slower time scale diffusion in a polymer matrix compared to liquid electrolytes.In this study, cyclic carbonate-based polymer electrolytes were synthesized to mimic the beneficial properties of conventional carbonate-based liquid electrolytes, such as high level of ion dissociation and solid electrolyte interphase (SEI) formation. A series of copolymers were synthesized varying the structure and composition of the anionic monomer and polar cyclic carbonate containing monomer. The tertiary hydrogen on these carbonate monomers can act as a crosslinking point in free radical polymerizations or UV curing processes to provide robust mechanical properties to the SPEs at elevated temperatures. Although the inherent conductivities of the single-ion SPEs are on the order of 10-7 mS/cm, the addition of plasticizers can improve these conductivities to 0.1 mS/cm.

Enhanced Safety, High-Rate and High-Voltage Performance of a Lithium-Ion Battery Using Nonflammable Liquid Electrolyte

These days lithium-ion battery (LIB) market is rapidly expanding by electric mobilities and stationary energy storage system industries. One of the biggest challenges in the research and development of advanced LIB is to achieve simultaneously outstanding energy density, cycle life, charge rate, and safety. For fast charging, battery chemistry and reaction kinetics are being evolved from the current hours scale toward minutes scale charging. In the LIB electrolyte perspective, the conventional carbonate-based liquid electrolyte has several limitations in safety and high-rate and high-voltage performance, due to low thermal and anodic stabilities under extreme operation conditions like high temperature, high-current, and high-voltage. To mitigate those issues, we have been developing new and safe electrolyte without any trade-off with cycling performance and energy density of Li-ion batteries. Herein, we present high-rate and high-voltage cycling performance and high safety of nickel-rich cathode-based lithium-ion full-cell fabricated with nonflammable liquid electrolyte. The correlation between the stability of nonflammable liquid electrolyte and its derived solid electrolyte interphase (SEI) and performance will be discussed in this meeting. Acknowledgements This research was supported by the National Research Foundation grant funded by the Ministry of Science and ICT (No. 2019R1A2C1084024).

Polyethylene glycol-grafted cellulose-based gel polymer electrolyte for long-life Li-ion batteries

Recently, highly abundant natural materials have been used in the fields of energy storage because of their environmental friendliness and low cost. However, use of some natural materials like cellulose as host matrices of gel polymer electrolytes (GPEs) is challenging owing to the strong intra- and inter-molecular hydrogen bonding. Herein, a green GPE film was prepared by chemically grafting soft chain-polyethylene glycol (PEG) onto the backbone of cellulose. The introduction of PEG significantly improved the toughness of cellulose from 118 × 103to 270 × 103kJ m−3, as well as raised the wettability in carbonate-based liquid electrolyte solutions from 22.6% to 141.7%. The first cycle coulomb efficiency stayed above 90%. The capacity retention of LiFePO4/Libatteries assembled with the as-obtained GPEreached 80.3% after 300 cycles at 0.2 C. In sum, the as-obtained cellulose-based GPEs look promising to replace separators and liquid electrolytes in Li-ion batteries.

Hollow-core optical fibre sensors for operando Raman spectroscopy investigation of Li-ion battery liquid electrolytes

Improved analytical tools are urgently required to identify degradation and failure mechanisms in Li-ion batteries. However, understanding and ultimately avoiding these detrimental mechanisms requires continuous tracking of complex electrochemical processes in different battery components. Here, we report an operando spectroscopy method that enables monitoring the chemistry of a carbonate-based liquid electrolyte during electrochemical cycling in Li-ion batteries with a graphite anode and a LiNi0.8Mn0.1Co0.1O2 cathode. By embedding a hollow-core optical fibre probe inside a lab-scale pouch cell, we demonstrate the effective evolution of the liquid electrolyte species by background-free Raman spectroscopy. The analysis of the spectroscopy measurements reveals changes in the ratio of carbonate solvents and electrolyte additives as a function of the cell voltage and show the potential to track the lithium-ion solvation dynamics. The proposed operando methodology contributes to understanding better the current Li-ion battery limitations and paves the way for studies of the degradation mechanisms in different electrochemical energy storage systems.

Poly(ethylene oxide)-Based Electrolytes for Solid-State Potassium Metal Batteries with a Prussian Blue Positive Electrode

Potassium-ion batteries are an emerging post-lithium technology that are considered ecologically and economically benign in terms of raw materials’ abundance and cost. Conventional cell configurations employ flammable liquid electrolytes that impose safety concerns, as well as considerable degrees of irreversible side reactions at the reactive electrode interfaces (especially against potassium metal), resulting in a rapid capacity fade. While being inherently safer, solid polymer electrolytes may present a solution to capacity losses owing to their broad electrochemical stability window. Herein, we present for the first time a stable solid-state potassium battery composed of a potassium metal negative electrode, a Prussian blue analogue K2Fe[Fe(CN)6] positive electrode, and a poly(ethylene oxide)-potassium bis(trifluoromethanesulfonyl)imide polymer electrolyte. At an elevated operating temperature of 55 °C, the solid-state battery achieved a superior capacity retention of 90% over 50 cycles in direct comparison to a conventional carbonate-based liquid electrolyte operated at ambient temperature with a capacity retention of only 66% over the same cycle number interval.

Poly (vinyl ethylene carbonate)-based dual-salt gel polymer electrolyte enabling high voltage lithium metal batteries

Rechargeable lithium metal batteries (LMBs) have been regarded as one of the most promising next-generation energy-storage systems due to their high theoretical energy density. However, the practical application of LMBs is greatly impeded by poor high-voltage tolerance and safety concerns originated from flammable organic carbonate-based liquid electrolytes. Herein, a novel dual-salt gel polymer electrolyte (DS-GPE) is prepared via in situ polymerization of vinyl ethylene carbonate (VEC) and pentaerythritol tetra acrylate (PETEA) monomers in a poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) porous structure. The newly developed DS-GPE shows high ionic conductivity (6.9 mS cm−1) at room temperature, adequate Li+ transference number (tLi+= 0.512), outstanding oxidative resistance (5.3 V vs. Li/Li+) and favorable interfacial compatibility. Stable interfacial layers are rich in B-, F-, components on both the Li metal anode and high-voltage LiCoO2 cathode, realizing excellent cycling stability in Li||Li symmetrical cells, and a capacity retention of 83.42% over 100 cycles with average Coulombic efficiency of 99.86% in Li||LiCoO2 cell.

Evolution of fluoride shuttle battery reactions and three-dimensional morphology changes of BiF3 microparticles in an ethylene carbonate-based liquid electrolyte

Fluoride shuttle battery reactions of BiF3 microparticles were observed in an ethylene carbonate-based electrolyte. The reaction mechanisms and rate-determining steps were elucidated.

(Invited) Enabling Reversible Plating and Stripping of Lithium Metal in Lithium Metal Batteries

Lithium metal batteries with lithium metal anodes have the potential to almost double the energy density of today's lithium-ion batteries. However, non-uniform lithium plating and stripping causes poor cycling stability, low Coulombic efficiency, potential safety issues, and has hindered the commercialization of lithium metal batteries at scale. We discuss several promising strategies to achieve stable lithium plating and stripping.We report a nanocomposite coating for the protection of lithium metal anodes, which consists of nano-sized LiF particles embedded into a PEO polymer matrix [1]. The composite offers a large LiF/PEO interface area throughout the coating, promoting exceptionally high lithium-ion conductivity of 0.97 mS cm–1 and high lithium-ion transference number of 0.77 at room temperature in contact with a carbonate-based liquid electrolyte. Both properties are key to realize uniform lithium plating and stripping and prevent lithium dendrite formation. Lithium metal electrodes coated with this protective coating enable stable lithium plating and stripping at 1 mA cm–2 for over 1000 h at room temperature. A full cell with the coated lithium metal anode and a NMC622 cathode with an areal capacity of 1 mAh cm–2 shows much improved specific capacity and cycling stability at high current density. The cell exhibits a high initial capacity of 135 mAh g–1 and 83% capacity retention after 500 cycles at 1 mA cm–2. Even at a high current density of 3 mA cm–2, the full cell shows an initial capacity of 125 mAh g–1 and 74% capacity retention after 300 cycles.We will also discuss challenges and opportunities to stabilize plating and stripping of lithium metal in all-solid-state batteries [2-4].[1] C. Fu and C. Battaglia, ACS Appl. Mater. Interf. 2020, 12, 41620[2] M. Bay, M. Wang, R. Grissa, M. V. F. Heinz, J. Sakamoto, and C. Battaglia, Adv. Energy Mater. 2019, 1902899[3] R. Grissa, S. Payandeh, M. Heinz, and C. Battaglia, ACS Appl. Mater. Interf. 2021, 13, 14700[4] F. Pagani, C. Fu, and C. Battaglia, in preparation

Highly conductive polymer electrolytes based on PAN-PEI nanofiber membranes with in situ gelated liquid electrolytes for lithium-ion batteries

The development of solid state electrolytes is considered as an effective approach to build safer lithium-ion batteries by replacing the conventional liquid electrolytes. However, the solid state electrolytes face continuous challenges to improve their ionic conductivities and mechanical properties. Herein, we report the synthesis of novel polymer electrolytes based on cross-linked polyacrylonitrile-polyethylenimine (PAN-PEI) nanofiber membranes infiltrated with in-situ gelated electrolytes using tripropylene glycol diacrylate as crosslinking agent in the organic carbonate-based liquid electrolytes. The PAN-PEI nanofiber membranes with different mass ratios of PAN/PEI prepared by electrospinning method are constructed with entangled nanofibers of an average diameter of ~600 nm. The optimized PAN-PEI based electrolyte has a high ionic conductivity up to 3.39 mS cm−1 at room-temperature and decent tensile strength of 9.36 MPa. Linear sweep voltammetry shows that the polymer electrolyte also has a wide electrochemical window of 5.4 V (vs. Li/Li+). This polymer electrolyte exhibits excellent cycling stability even in the high energy density of LiNi0.8Co0.1Mn0.1O2/Graphite, delivering an initial discharge capacity of 175 mAh g−1 at 0.5 C with a capacity retention of 91.4% after 200 cycles.

Influence of synthesis parameters on crystallization behavior and ionic conductivity of the Li4PS4I solid electrolyte

Superionic solid electrolytes are key to the development of advanced solid-state Li batteries. In recent years, various materials have been discovered, with ionic conductivities approaching or even exceeding those of carbonate-based liquid electrolytes used in high-performance Li-ion batteries. Among the different classes of inorganic solid electrolytes under study, lithium thiophosphates are one of the most promising due to their high Li-ion conductivity at room temperature and mechanical softness. Here, we report about the effect of synthesis parameters on the crystallization behavior and charge-transport properties of Li4PS4I. We show that thermally induced crystallization of Li4PS4I (P4/nmm), starting from the glassy phase 1.5Li2S–0.5P2S5–LiI, adversely affects the material’s conductivity. However, both conductivity and crystallization temperature can be significantly increased by applying pressure during the preparation.