Electrolyte Lithium Research Articles

Stable Anodeless Solid-State Batteries Enabled by Carbon-Metal Based Artificial Interface

Anodeless system maximizes all-solid-state batteries’ advantages of energy density and stability. Sulfide-based solid electrolytes exhibit high ionic conductivity and processability, but the narrow electrochemical stability window causes electrolyte decomposition. A preferential strategy to suppress electrolyte decomposition is limiting contact area between lithium metal and electrolyte by the introduction of protective layer, such as carbon-metal layer, between the current collector and the sulfide-based electrolyte layer is one example. In this presentation, we report protective capability of carbon only layer and carbon-metal layer using various electrochemical and analytical characterization technics. Cross sectional images of charged, discharged state of these two anodeless systems demonstrate carbon-metal layer could regulate the site for lithium plating and spatially separate the solid state electrolyte and lithium deposited layer. From these results, we will discuss the key parameters for stable operation of Li metal free anode for all solid-state battery systems.

Construction of a Bis(benzene sulfonyl)imide-Based Single-ion Polymer Artificial Layer for a Steady Lithium Metal Anode.

Dendrite growth and parasitic reactions with liquid electrolyte are the two key factors that restrict the practical application of the lithium metal anode. Herein, a bis(benzene sulfonyl)imide based single-ion polymer artificial layer for a lithium metal anode is successfully constructed, which is prepared via blending the as-prepared copolymer of lithiated 4, 4'-dicarboxyl bis(benzene sulfonyl)imide and 4,4'-diaminodiphenyl ether on the surface of lithium foil. This single-ion polymer artificial layer enables compact structure with unique continuous aggregated Li+ clusters, thus reducing the direct contact between lithium metal and electrolyte simultaneously, ensuring Li+ transport is fast and homogeneous. Based on which, the coulombic efficiency of the Li|Cu half-cell is effectively improved, and the cycle stability of the Li|Li symmetric cell can be prolonged from 160 h to 240 h. Surficial morphology and elemental valence analysis confirm that the bis(benzene sulfonyl)imide based single-ion polymer artificial layer effectively facilitates the Li+ uniform deposition and suppresses parasitic reactions between lithium metal anode and liquid electrolyte in the LFP|Li full-cell. This strategy provides a new perspective to achieve a steady lithium metal anode, which can be a promising candidate in practical applications.

Perspective on the mechanism of mass transport-induced (tip-growing) Li dendrite formation by comparing conventional liquid organic solvent with solid polymer-based electrolytes

A major challenge of Li metal electrodes is the growth of high surface area lithium during Li deposition with a variety of possible shapes and growing mechanisms. They are reactive and lead to active lithium losses, electrolyte depletion and safety concerns due to a potential risk of short-circuits and thermal runaway. This work focuses on the mechanism of tip-growing Li dendrite as a particular high surface area lithium morphology. Its formation mechanism is well-known and is triggered during concentration polarization, i.e. during mass (Li+) transport limitations, which has been thoroughly investigated in literature with liquid electrolytes. This work aims to give a stimulating perspective on this formation mechanism by considering solid polymer electrolytes. The in-here shown absence of the characteristic “voltage noise” immediately after complete concentration polarization, being an indicator for tip-growing dendritic growth, rules out the occurrence of the particular tip-growing morphology for solid polymer electrolytes under the specific electrochemical conditions. The generally poorer kinetics of solid polymer electrolytes compared to liquid electrolytes imply lower limiting currents, i.e. lower currents to realize complete concen­tration polarization. Hence, this longer-lasting Li-deposition times in solid polymer electro­lytes are assumed to prevent tip-growing mechanism via timely enabling solid electrolyte interphase formation on fresh Li deposits, while, as stated in previous literature, in liquid electrolytes, Li dendrite tip-growth process is faster than solid electrolyte interphase forma­tion kinetics. It can be reasonably concluded that tip-growing Li dendrites are in general practically unlikely for both, (i) the lower conducting electrolytes like solid polymer electro­lytes due to enabling solid electrolyte interphase formation and (ii) good-conducting electro­lytes like liquids due to an impractically high current required for concentration polarization.

A review of the use of Mxenes as hosts in lithium metal anodes and the anode formation

Severe dendritic growth and volume expansion are easily induced during the cycling process when lithium metal is used as an anode electrode directly. These problems cause the solid electrolyte interface (SEI) layer to break and re-form, which consumes the active lithium metal and electrolyte, thereby reducing the Coulomb efficiency and rapid capacity. Designing a host matrix with rapid mass transfer and enough storage space to promote lithium homogeneous deposition, hence reducing the repeated SEI growth and the formation of dead lithium, is an effective method to address the concerns mentioned above issues. MXenes with two-dimensional layered structures have been regarded as feasible hosts for stabilizing lithium due to their superior electrical conductivity, sizeable interlayer space, abundant lithiophilic surface functional groups, and excellent mechanical properties. In this review, we first summarized the multiple synthesis methods of MXenes, including etching the precursor MAX phase, chemical vapor deposition, UV-induced etching, and mechanochemical et al. Various synthesis methods would induce different surface termination and lamellar structures, affecting lithium metal nucleation and growth behavior. Subsequently, pure MXene, MXene-carbon and MXene-non carbon hybrid compounds applied for lithium metal anode hosts were introduced, focusing on alleviating noticeable volume changes and inhibiting lithium dendrite growth. Finally, some modification strategies and potential research prospects were summarized and prospected.

Structure‐mechanical properties correlation in bulk LiPON glass produced by nitridation of metaphosphate melts

AbstractThe glassy solid electrolyte Lithium phosphorous oxynitride (LiPON) has been widely researched in thin film solid state battery format due to its outstanding stability when cycled against lithium. In addition, recent reports show thin film LiPON having interesting mechanical behaviors, especially its ability to resist micro‐scale cracking via densification and shear flow. In the present study, we have produced bulk LiPON glasses with varying nitrogen contents by ammonolysis of LiPO3 melts. The resulting compositions were determined to be LiPO3‐3z/2Nz, where 0 ≤ z ≤ 0.75, and the z value of 0.75 is among the highest ever reported for this series of LiPON glasses. The short‐range order structures of the different resulting compositions were characterized by infrared, Raman, 31P magic angle spinning nuclear magnetic resonance, and X‐ray photoelectron spectroscopies. Instrumented nano‐indentation was used to measure mechanical properties. It was observed that similar to previous studies, both trigonally coordinated (Nt) and doubly bonded (Nd) N co‐exist in the glasses in about the same amounts for z ≤ 0.36, the limit of N content in most previous studies. For glasses with z > 0.36, it was found that the fraction of the Nt increased significantly while the fraction of Nd correspondingly decreased. The incorporation of nitrogen increased both the elastic modulus and hardness of the glass by approximately a factor of 1.5 when N/P ratio reaches 0.75. At the same time, an apparent embrittlement of the glass was observed due to nitridation, which was revealed by nanoindentation with an extra sharp nanoindenter tip.

Two-in-one structure as both lithium protective layer and electrolyte for safe solid-state lithium-metal battery

Demands for safe and compact electrochemical energy storage inspire hot pursuit of development of solid-state lithium-metal batteries (SSLMBs). However, several challenges, including high reaction activity of lithium metal anode and suboptimal comprehensive performance of solid-state electrolytes, hinder SSLMBs for broad applications. Herein, we propose the ingenious construction and application of polyvinylidene chlorid-based composite (PVDCC) as a two-in-one functional material that simultaneously protects the lithium metal anode from air/water corrosions and acts as solid-state electrolyte. On the basis of standout barrier and fine ion-permeability of PVDC, the as-constructed PVDC-based composite exhibits both excellent high air/water stability and high ionic conductivity in wide temperature range (e.g., 5.02 × 10−4 S cm−1 at 25 °C and 3.92 × 10−4 S cm−1 at 0 °C), thus contributing to remakable electrochemical performances in SSLMB, especially under a low temperature. For instance, at 0 °C, a reversible average discharge capacity of 95 mAh g−1 at 0.3 C with high capacity retention (99%) after 300 cycles can be accomplished. More encouragingly, the PVDCC with two-in-one functionality enables the access of assembling safe SSLMBs in ambient air. This proof-of-concept study offers fresh insights for tailoring the functional materials with both effective lithium protective layer and advanced solid-state electrolyte to facilely achieve high-performance SSLMBs.

Recent Progress on Electrolyte Boosting Initial Coulombic Efficiency in Lithium‐Ion Batteries

AbstractThe initial Coulombic efficiency (ICE) of electrode materials is closely related to the energy density of lithium‐ion batteries (LIBs). However, some promising electrode materials for next generation LIBs suffer from low ICE, which inevitably hinders their practical application. Among the discovered modified strategies for LIBs, electrolyte optimization has attracted extensive attention due to its facile operation process. Herein, the role of ICE in LIBs is first analyzed. Subsequently, the recent progress on effective electrolyte optimization strategies for boosting ICE in LIB is summarized (including the optimization of lithium salt, salt concentration, solvent, and electrolyte additive). Finally, future research directions of electrolyte optimization for boosting ICE are proposed. This review provides valuable guidance for developing advanced electrolyte for LIBs.

High-resolution isotopic analysis of lithium by micro laser-induced breakdown self-reversal isotopic spectrometry (LIBRIS) for isotopic labelling of lithium in solid-state electrolyte of lithium batteries

In order to improve the safety of Li-ion batteries, solid-state electrolytes have been studied for many years. However, lithium is known to have lower diffusion coefficients in these materials. Various methods can be used to investigate lithium transport mechanisms; one of them relies on isotopic tracing. This method often used in environmental sciences, medicine and biology has been developed since 2011 by Lu et al. in the battery field. In addition to the techniques commonly used for isotopic analysis of lithium in battery materials, such as nuclear magnetic resonance (NMR) and mass spectrometry techniques, a new complementary method for determining the spatial distribution of the lithium isotopic ratio in solid electrolytes has been developed: laser induced self-reversal isotopic spectrometry (LIBRIS) proposed by Touchet et al. in 2020. In this paper, a proof of concept of LIBRIS analysis of a solid electrolyte composed of poly(ethylene oxide) (POE) containing 6Li enriched lithium bis(trifluoromethylsulphonyl)imide (LiTFSI) was first achieved. Then, the lateral resolution of LIBRIS measurements was improved from 250 μm down to 7 μm. Such lateral resolution is well adapted to future studies of lithium transport mechanisms in a solid electrolyte composed of a dispersion of ceramic microparticles in a polymer matrix. This material design is used as a trade-off to improve Li diffusion compared to polymer-based electrolytes. The sources of signal fluctuations were discussed, and a calibration curve of the 6Li isotopic abundance in POE/LiTFSI samples was finally obtained, with a relative uncertainty of 25%. The results demonstrate the feasibility of high resolution isotopic analysis by the LIBRIS technique and could be applied in the future to the characterization of the lithium mobility in battery materials.

Mass transport and charge transfer through an electrified interface between metallic lithium and solid-state electrolytes

All-solid-state Li-ion batteries are one of the most promising energy storage devices for future automotive applications as high energy density metallic Li anodes can be safely used. However, introducing solid-state electrolytes needs a better understanding of the forming electrified electrode/electrolyte interface to facilitate the charge and mass transport through it and design ever-high-performance batteries. This study investigates the interface between metallic lithium and solid-state electrolytes. Using spectroscopic ellipsometry, we detected the formation of the space charge depletion layers even in the presence of metallic Li. That is counterintuitive and has been a subject of intense debate in recent years. Using impedance measurements, we obtain key parameters characterizing these layers and, with the help of kinetic Monte Carlo simulations, construct a comprehensive model of the systems to gain insights into the mass transport and the underlying mechanisms of charge accumulation, which is crucial for developing high-performance solid-state batteries.

Solid polymer electrolytes: Ion conduction mechanisms and enhancement strategies

Solid polymer electrolytes (SPEs) possess comprehensive advantages such as high flexibility, low interfacial resistance with the electrodes, excellent film-forming ability, and low price, however, their applications in solid-state batteries are mainly hindered by the insufficient ionic conductivity especially below the melting temperatures, etc. To improve the ion conduction capability and other properties, a variety of modification strategies have been exploited. In this review article, we scrutinize the structure characteristics and the ion transfer behaviors of the SPEs (and their composites) and then disclose the ion conduction mechanisms. The ion transport involves the ion hopping and the polymer segmental motion, and the improvement in the ionic conductivity is mainly attributed to the increase of the concentration and mobility of the charge carriers and the construction of fast-ion pathways. Furthermore, the recent advances on the modification strategies of the SPEs to enhance the ion conduction from copolymer structure design to lithium salt exploitation, additive engineering, and electrolyte micromorphology adjustion are summarized. This article intends to give a comprehensive, systemic, and profound understanding of the ion conduction and enhancement mechanisms of the SPEs for their viable applications in solid-state batteries with high safety and energy density.

A New Desiccant Based on Graphene Oxide for Deep Dehydration of Electrolytes for Electrochemical Cells

A material based on graphene oxide is considered as a desiccant of aprotic solvents in nonaqueous electrolytes containing lithium salts. Three methods are proposed for preparation of final materials with different number and volume of pores. The effect of the initial parameters of hydrogel such as its pH and the concentration of solid substance is studied. Dependences of the adsorption capacity of desiccant on its porosity are plotted. The prospects of this new desiccant in dehydration of lithium electrolytes are discussed as compared with commercial molecular sieves.

Origin of Heterogeneous Stripping of Lithium in Liquid Electrolytes.

Lithium metal batteries suffer from low cycle life. During discharge, parts of the lithium are not stripped reversibly and remain isolated from the current collector. This isolated lithium is trapped in the insulating remaining solid-electrolyte interphase (SEI) shell and contributes to the capacity loss. However, a fundamental understanding of why isolated lithium forms and how it can be mitigated is lacking. In this article, we perform a combined theoretical and experimental study to understand isolated lithium formation during stripping. We derive a thermodynamic consistent model of lithium dissolution and find that the interaction between lithium and SEI leads to locally preferred stripping and isolated lithium formation. Based on a cryogenic transmission electron microscopy (cryo TEM) setup, we reveal that these local effects are particularly pronounced at kinks of lithium whiskers. We find that lithium stripping can be heterogeneous both on a nanoscale and on a larger scale. Cryo TEM observations confirm our theoretical prediction that isolated lithium occurs less at higher stripping current densities. The origin of isolated lithium lies in local effects, such as heterogeneous SEI, stress fields, or the geometric shape of the deposits. We conclude that in order to mitigate isolated lithium, a uniform lithium morphology during plating and a homogeneous SEI are indispensable.

A novel flame-retardant nitrile-based gel polymer electrolyte for quasi-solid-state lithium metal batteries

In this work, a novel type of highly Li+-ions conductive, nonflammable adiponitrile (ADN)-based gel polymer electrolyte (denoted as AT11-GF) was prepared as a promising solid-state electrolyte for lithium (Li)-metal batteries by in-situ polymerization method. In order to overcome the parasitic reactions of ADN and triethyl phosphate (TEP) on Li-anode surface, fluoroethylene carbonate (FEC) was utilized as film-forming agent to generate LiF-enrich interface in this system of ADN-based electrolyte. The as-prepared electrolyte exhibited high ionic conductivity of 1.724 × 10−3 S/cm at ambient temperature, wide electrochemical window (∼5.75 V vs. Li+/Li), favorable Li+-ion transfer number (tLi+=0.70), and superior interfacial compatibility with Li anode (ultra-stable at a current density of 0.2 mA/cm2 for 1000 h). The LiFePO4|AT11-GF|Li battery presented an excellent rate capacity of 116.9 mAh/g at 2.0 C, and long-term cycling performance with a specific capacity of 134.6 mAh/g and a capacity retention of 94.5% after 1000 cycles at a current density of 1.0 C. Therefore, this as-prepared ADN-based electrolyte exhibited great promise for the application in solid-state Li-metal batteries.

Advances in Ordered Architecture Design of Composite Solid Electrolytes for Solid-State Lithium Batteries.

Solid electrolyte lithium batteries are the next generation of advanced energy devices. The incorporation of solid electrolytes can significantly improve the safety issue of lithium-ion batteries. Organic-inorganic composite solid electrolytes (CSE) are promising candidates for solid-state batteries, but their application is mainly limited by low ionic conductivity. Many studies have shown that the architecture of ordered inorganic fillers in CSE can act as fast lithium-ion transfer channels by auxiliary means, thus significantly improving the ionic conductivities. This review summarises the recent advances in CSE with different dimensional inorganic fillers. Various effective strategies for the construction of ordered structures in CSE are then presented. The review concludes with an outlook on the future development of CSE. This review aims to provide researchers with an in-depth understanding of how to achieve ordered architectures in CSE for advanced solid state lithium batteries.

Machine-Learning Approaches for the Discovery of Electrolyte Materials for Solid-State Lithium Batteries

Solid-state lithium batteries have attracted considerable research attention for their potential advantages over conventional liquid electrolyte lithium batteries. The discovery of lithium solid-state electrolytes (SSEs) is still undergoing to solve the remaining challenges, and machine learning (ML) approaches could potentially accelerate the process significantly. This review introduces common ML techniques employed in materials discovery and an overview of ML applications in lithium SSE discovery, with perspectives on the key issues and future outlooks.

In situ Synthesis of Gel Polymer Electrolytes for Lithium Batteries

AbstractGel polymer electrolytes (GPEs) are considered as a promising solution to replace organic liquid electrolytes for safer lithium (Li) batteries due to their high ionic conductivity comparable to liquid electrolytes, no risk of leakage, and high flexibility. However, poor interfacial contact between electrodes and GPEs leads to high interfacial impedance and unsatisfactory electrochemical performance. The emerging in situ synthesized GPEs can fully infiltrate into porous electrodes and form intimate interfaces, improving interfacial contact and electrochemical performance. This perspective covers recent advances of in situ GPEs in design, synthesis, and applications in lithium (Li) batteries. Polyester and polyether‐based GPEs are mainly discussed followed by a brief introduction of GPEs with other polymer matrices, such as poly(ionic liquid)s, cyanoethyl polyvinyl alcohol, poly(vinyl acetal) and single‐ion conductors. Then, the recent progress in Li batteries using in situ GPEs are summarized, including Li‐ion battery, Li‐metal battery, Li‐sulfur battery, and Li‐air battery. Finally, the remaining challenges and future perspectives of in situ GPEs are discussed. We hope this perspective can offer guidance for in situ synthesis of GPEs and facilitate their applications in high‐performance Li batteries.

Multifunctional asymmetric electrolyte membrane encouraging durable lithium-metal batteries in wide temperature variations

The progress of high-performance lithium-metal batteries (LMBs) has been greatly impeded by lithium dendrite growth and electrolyte performance defects. Herein, an ultra-thin asymmetric multilayer composite electrolyte with a total thickness of 19 μm is designed. The rigid metal-organic framework (MOF) tier with Li+ conductivity towards the anode side adjusts the even deposition of Li+, owns high elasticity modulus (6.4 GPa) to restrain lithium dendrite formation, and improves the thermostability of the membrane. The in-situ cross-linked polymer layer on the cathode side achieves good electrode-electrolyte interface contact. Consequently, the functional asymmetric multilayer composite electrolyte displays a superior ionic conductivity (0.68 mS cm−1) and a high-efficiency Li+ transference (tLi+ = 0.47). The assembled Li||Li symmetric cells can cycle steadily for 1500 h at a high current density of 3 mA cm−2 at 30 °C and 1000 h at 1 mA cm−2 at 100 °C. The assembled LMBs with different cathodes show high rate capability and long-period cycling stability at room temperature. More impressively, the batteries display excellent electrochemical performance within −15 °C-100 °C and do not cause a short circuit even at 170 °C, showing high thermal safety. This work frames a neoteric strategy for the practical application of LMBs.

Intermolecular Interactions Mediated Nonflammable Electrolyte for High‐Voltage Lithium Metal Batteries in Wide Temperature

AbstractHigh‐voltage lithium metal batteries are the most promising energy storage technology due to their excellent energy density (>400 Wh kg−1). However, the oxidation decomposition of conventional carbonate‐based electrolytes at the high‐potential cathode, the detrimental reaction between the lithium anode and electrolyte, particularly the uncontrolled lithium dendrite growth, always lead to a severe capacity decay and/or flammable safety issues, hindering their practical applications. Herein, a solvation structure engineering strategy based on tuning intermolecular interactions is proposed as a strategy to design a novel nonflammable fluorinated electrolyte. Using this approach, this work shows superior cycling stability in a wide temperature range (−40 °C to 60 °C) for a 4.4 V‐class LiNi0.8Co0.1Mn0.1O2 (NCM811)‐based Li‐metal battery. By coupling the high‐loading of NCM811 cathode (3.0 mAh cm−2) and a controlled amount of lithium anode (twofold excess of Li deposition on Cu, Cu@Li) (N/P = 2), the Cu@Li || NCM811 full cell can cycle more than 162 cycles with high‐capacity retention of 80%. This work finds that the change of the coordination environment of Li+ with solvent and PF6− by tuning intermolecular interaction is an effective method to stabilize the electrolyte and electrode performance. These discoveries can provide a pathway for electrolyte design in metal ion batteries.

Manipulating Li2 S Redox Kinetics and Lithium Dendrites by Core-Shell Catalysts under High Sulfur Loading and Lean-Electrolyte Conditions.

For practical lithium-sulfur batteries (LSBs), the high sulfur loading and lean-electrolyte are necessary conditions to achieve the high energy density. However, such extreme conditions will cause serious battery performance fading, due to the uncontrolled deposition of Li2 S and lithium dendrite growth. Herein, the tiny Co nanoparticles embedded N-doped carbon@Co9 S8 core-shell material (CoNC@Co9 S8 NC) is designed to address these challenges. The Co9 S8 NC-shell effectively captures lithium polysulfides (LiPSs) and electrolyte, and suppresses the lithium dendrite growth. The CoNC-core not only improves electronic conductivity, but also promotes Li+ diffusion as well as accelerates Li2 S deposition/decomposition. Consequently, the cell with CoNC@Co9 S8 NC modified separator delivers a high specific capacity of 700 mAh g-1 with a low-capacity decay rate of 0.035% per cycle at 1.0 C after 750 cycles under a sulfur loading of 3.2mg cm-2 and a E/S ratio of 12µL mg-1 , and a high initial areal capacity of 9.6 mAh cm-2 under a high sulfur loading of 8.8mg cm-2 and a low E/S ratio of 4.5µL mg-1 . Besides, the CoNC@Co9 S8 NC exhibits an ultralow overpotential fluctuation of 11mV at a current density of 0.5mA cm-2 after 1000h during a continuous Li plating/striping process.

Synergistic interactions between the charge‐transport and mechanical properties of the ionic‐liquid‐based solid polymer electrolytes for solid‐state lithium batteries

AbstractThe performance sensitivity of the solid‐state lithium cells to the synergistic interactions of the charge‐transport and mechanical properties of the electrolyte is well acknowledged in the literature, but the quantitative insights therein are very limited. Here, the charge‐transport and mechanical properties of a polymerized ionic‐liquid‐based solid electrolyte are reported. The transference number and diffusion coefficient of lithium in the concentrated solid electrolyte are measured as a function of concentration and stack pressure. The elastoplastic behavior of the electrolyte is quantified under compression, within a home‐made setup, to substantiate the impact of stack pressure on the stability of the Li/electrolyte interface in the symmetric lithium cells. The results spotlight the interaction between the concentration and thickness of the solid electrolyte and the stack pressure in determining the polarization and stability of the solid‐state lithium batteries during extended cycling.