Performance Of Lithium Metal Batteries Research Articles

Separator Wettability Enhanced by Electrolyte Additive to Boost the Electrochemical Performance of Lithium Metal Batteries

Lithium (Li) metal has been regarded as one of the most promising candidates to replace graphite anode due to its high theoretical specific capacity and the lowest electrochemical potential [1,2,3]. However, the immoderate growth of Li dendrite during Li plating/stripping causes serious safety problem and poor performance that severely impedes the practical application of lithium metal batteries (LMBs) [4,5,6]. Until now, there have been numerous kinds of strategies be proposed to inhibit Li dendrites growth and protect lithium metal anode such as high concentration electrolytes [7], construction of the solid electrolyte interface layer [8], structural design of anode materials [9], regulation of Li+ solvation [10], and solid-state electrolytes [11]. As an important part of battery structure, separator plays a vital role in the performance of battery [12]. The main function of separator is to divide the anode and cathode that prevents internal short circuit caused by direct contact between anode and cathode. So, the separator needs to be electrically insulated. At the same time, the separator also needs to ensure that the electrolyte is conductive between anode and cathode [13]. Therefore, it is necessary to render the separator fully wetted. Nevertheless, there are few researches on enhancing the wettability of the separator especially functional electrolyte additives.

Quantitatively Designing Porous Copper Current Collectors for Lithium Metal Anodes

Author(s): Lu, B; Olivera, E; Scharf, J; Chouchane, M; Fang, C; Ceja, M; Pangilinan, LE; Zheng, S; Dawson, A; Cheng, D; Bao, W; Arcelus, O; Franco, AA; Li, X; Tolbert, SH; Meng, YS | Abstract: Lithium metal has been an attractive candidate as a next-generation anode material. Despite its popularity, stability issues of lithium in the liquid electrolyte and the formation of lithium whiskers have kept it from practical use. Three-dimensional (3D) current collectors have been proposed as an effective method to mitigate whisker growth. Although extensive research has been done, the effects of three key parameters of the 3D current collectors, namely, the surface area, the tortuosity factor, and the surface chemistry, on the performance of lithium metal batteries remain elusive. Herein, we quantitatively studied the role of these three parameters by synthesizing four types of porous copper networks with different sizes of well-structured microchannels. X-ray microscale computed tomography (micro-CT) allowed us to assess the surface area, the pore size, and the tortuosity factor of the porous copper materials. A metallic Zn coating was also applied to study the influence of surface chemistry on the performance of the 3D current collectors. The effects of these parameters on the performance were studied in detail through scanning electron microscopy (SEM) and titration gas chromatography (TGC). Stochastic simulations further allowed us to interpret the role of the tortuosity factor in lithiation. The optimal range of the key parameters is thereby found for the porous coppers and their performance is predicted. Using these parameters to inform the design of porous copper anodes for Li deposition, Coulombic efficiencies (CEs) of up to 99.63% are achieved, thus paving the way for the design of effective 3D current collector systems.

Formation mechanism of the solid electrolyte interphase in different ester electrolytes

The solid electrolyte interphase (SEI) plays a critical role in determining the performance of lithium metal batteries.

(Europe Section Alessandro Volta Medal Award) Electrolytes and Metallic Anodes: About an Old Argument That Marks the Fundamental Understanding of Modern Metal Anodes in Advanced Battery Systems

Simple, yet meaningful, experiments, already carried out in the 18th century by Galvani and Volta, are at the very base of modern batteries that shape our society. From the very first muscle twitch to batteries found nowadays in nearly every part of modern life, with the best known example of a modern battery represented by the lithium ion battery (LIB), the same basic principles are present. The comparably fast and seminal development of LIBs through assiduous collective efforts was granted the 2019 Nobel Prize in Chemistry.[1] Besides all modern perspectives, fundamental principles are still being derived from the early works of Volta and Galvani, which have not been always in agreement.Because the LIB technology is more and more approaching its ceiling in terms of specific energy (Wh kg−1) and energy density (Wh L−1) imposed by the nature of intercalation chemistry, metal-based anodes, such as Li, Na, Mg, Ca, Zn and Al, are currently considered for the next evolutional step of battery technology.[2,3,4] Independent of the chosen materials, the chemistry of the anodes (graphite, silicon or metal anodes) with the electrolyte plays a crucial role in the development of the batteries. In LIBs, the formation of a solid electrolyte interphase (SEI) on graphite in organic media induced by an external current/voltage and involving the reduction of the electrolyte components was key for the stable operation of such anodes.[5] Similar processes for metal-based anodes do not necessarily require electrode polarization conditions and can occur spontaneously. For example, supplementary to SEI formation on the Li surface, induced by the extremely low redox potential of metallic lithium (−3.04 V vs. SHE), other processes of Li deterioration, namely galvanic corrosion (worth also considering here: dendrite growth, volume changes of the Li anode, low Coulombic efficiency), have to be scrutinized. Recently, battery researchers revisited the corrosion phenomena in lithium metal batteries (LMBs).[6,7] A systematic study focused on the corrosion-related processes in model Li anodes (using Li powder) revealed the great significance that such processes exercise on the performance of LMBs.[7]From a different perspective, flammable non-aqueous electrolytes, widely used in the LIB/LMB systems, are causing increased safety concerns. As an alternative, Zn has been regarded as a potential anode material for aqueous batteries because of its high theoretical volumetric capacity and suitable redox potential (−0.76 V vs. SHE), along with an intrinsic safety from the aqueous electrolyte nature. Similar to the Li anode in nonaqueous electrolytes, the Zn anode has also long-standing challenges in conventional alkaline electrolytes, such as chemical instability (e.g. corrosion) and electrochemical irreversibility (e.g. non-uniform electrodeposition/-dissolution, dendrite growth).[8]In this perspective, the two worlds of Li-based and Zn-based battery systems are united and attributed to the lessons by Volta and Galvani. Metals from the Volta pile (Cu and Zn) and modern metals (Li) are discussed side by side and in correlation to each other. Solutions to address their challenges, and thus overcome the barriers of their application, in rechargeable systems will be highlighted. It is emphasized that the combination of metals (e.g. Li) with metal ions (e.g. Zn2+) can result in formation of intermetallic phases, able to improve stability of the electrodes under cell operation conditions. This can further result in an increase in safety and cycle life of the batteries utilizing metals as negative electrodes.[9] Special attention will be also given to the obstacles caused by the alkaline electrolytes with focus on the fundamental understanding of Zn reaction mechanisms. Approaches to overcome the challenges are presented and evaluated for their potential to facilitate further research and development of electrolytes in these systems.

Hybrid Effect of Micro-Patterned Lithium Metal and Three Dimensionally Ordered Macroporous Polyimide Separator on the Cycle Performance of Lithium Metal Batteries

Short cycle life of the lithium metal secondary battery (LMSB) is largely ascribed to the dendritic growth of lithium metal during the charging process followed by continuous electrolyte decomposition. To make up for this intrinsic drawback of lithium metal, two pioneering techniques, micropatterning on lithium metal and three dimensionally ordered microporous polyimide (3DOM PI) separator, are combined to ascertain their hybrid effect on the cycle performance of LMSB. When a unit cell consisting of LiNi0.6Mn0.2Co0.2O2/3DOM PI separator/patterned lithium metal is cycled at the charging and discharging c-rates of 0.3C and 1C (1C = 2.5 mA), respectively, above 80% of the initial discharge capacity is maintained even after 400 cycles, while a control cell with polyethylene separator survives only for 130 cycles. This tremendous improvement is ascribed to the combination effect of inducing preferential lithium electrodeposition reaction into the micropattern and the uniform distribution of lithium ions on the nonpatterned lithium surface region by the 3DOM PI separator. Thus, combining these two technologies is very promising for LMSB commercialization in the future.

Ionic liquids for high performance lithium metal batteries

The pursuit of high energy density has promoted the development of high-performance lithium metal batteries. However, it faces a serious security problem. Ionic liquids have attracted great attention due to their high ionic conductivity, non-flammability, and the properties of promoting the formation of stable SEI films. Deeply understanding the problems existing in lithium metal batteries and the role of ionic liquids in them is of great significance for improving the performance of lithium metal batteries. This article reviews the effects of the molecular structure of ionic liquids on ionic conductivity, Li+ ion transference number, electrochemical stability window, and lithium metal anode/electrolyte interface, as well as the application of ionic liquids in Li-high voltage cathode batteries, Li-O2 batteries and Li-S batteries. The molecular design, composition and polymerization will be the main strategies for the future development of ionic liquid-based electrolytes for high performance lithium metal battery.

High-performance all-solid-state polymer electrolyte with fast conductivity pathway formed by hierarchical structure polyamide 6 nanofiber for lithium metal battery

Abstract The utilization of all-solid-state electrolytes is considered to be an effective way to enhance the safety performance of lithium metal batteries. However, the low ionic conductivity and poor interface compatibility greatly restrict the development of all-solid-state battery. In this study, a composite electrolyte combining the electrospun polyamide 6 (PA6) nanofiber membrane with hierarchical structure and the polyethylene oxide (PEO) polymer is investigated. The introduction of PA6 nanofiber membrane can effectively reduce the crystallinity of the polymer, so that the ionic conductivity of the electrolyte can be enhanced. Moreover, it is found that the presence of finely branched fibers in the hierarchical structure PA6 membrane allows the polar functional groups (C=O and N−H bonds) to be fully exposed, which provides sufficient functional sites for lithium ion transport and helps to regulate the uniform deposition of lithium metal. Moreover, the hierarchical structure can enhance the mechanical strength (9.2 MPa) of the electrolyte, thereby effectively improving the safety and cycle stability of the battery. The prepared Li/Li symmetric battery can be stably cycled for 1500 h under 0.3 mA cm−2 and 60 °C. This study demonstrates that the prepared electrolyte has excellent application prospects in the next generation all-solid-state lithium metal batteries.

Flexible, Self-Healing, and Fire-Resistant Polymer Electrolytes Fabricated via Photopolymerization for All-Solid-State Lithium Metal Batteries.

The cyclophosphazene-based self-healing polymer electrolytes (CPSHPE) is designed and fabricated via the copolymerization of hexa(4-ethyl acrylate phenoxy) cyclotriphosphazene (HCP), (2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate) (UPyMA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) under UV irradiation. The cross-linking structure formed by HCP could effectively enhance the mechanical strength of the polymer electrolyte, and the cyclotriphosphazene as the core is able to improve the flame-retardant properties. Benefiting from the phenyl groups in HCP and the cross-linking structure, the CPSHPE shows high thermal stability (up to 300 °C). On the other hand, the supramolecular network fabricated by the dynamic ureido-pyrimidinone (UPy) dimers endows the polymer electrolyte with good self-healing capability and is expected to improve the reliability of polymer lithium batteries. Moreover, the cells were fabricated with LiFePO4 (LFP), CPSHPE, and Li anodes show good reversible specific capacity. The CPSHPE could be a promising candidate as the multifunctional polymer electrolyte to improve the safety performance of lithium metal batteries.

Hybrid Effect of Micropatterned Lithium Metal and Three Dimensionally Ordered Macroporous Polyimide Separator on the Cycle Performance of Lithium Metal Batteries

Short cycle life of the lithium metal secondary battery (LMSB) is largely ascribed to the dendritic growth of lithium metal during the charging process followed by continuous electrolyte decomposit...

Sulfur‐Rich Molybdenum Sulfide as an Anode Coating to Improve Performance of Lithium Metal Batteries

AbstractIn lithium metal batteries (LMBs), the reaction between metallic Li and organic electrolytes consumes both Li and electrolyte, while the inhomogeneity of the resulting solid‐electrolyte interphase (SEI) contributes to inhomogeneous Li deposition. An artificial SEI, made by coating the Li surface with an electronically insulating material, can mitigate problems caused by uncontrolled SEI formation by 1) decreasing reduction of the electrolyte on the surface, and 2) increasing the uniformity of the Li+ flux to the electrode surface, thereby mitigating dendrite growth. In this work, we present a technique for coating the surface of LMB electrodes with sulfur‐rich molybdenum sulfide. This coating acts as an artificial SEI, which improves the coulombic efficiency and cycling stability of the LMBs by improving the reaction kinetics and decreasing the surface area of the exposed Li.

Co-guiding the dendrite-free plating of lithium on lithiophilic ZnO and fluoride modified 3D porous copper for stable Li metal anode

Lithium metal battery is considered to be the most promising energy storage technologies due to its ultra-high theoretical capacity and extremely low standard potential. However, the infinite volume change during uneven deposition/dissolution process and the growth of lithium dendrite resulting in severe capacity decay and high safety hazards, which hinders the application in next generation secondary batteries. In this paper, the three dimensional (3D) porous copper is prepared through an electrochemical etching CuZn alloy, and the pore walls are modified with lithiophilic layer of ZnO and fluorine. The as-prepared 3D Cu/ZnO/F can inhibit the growth of Li dendrite and mitigate the huge volume change of Li metal anode during cycling process, resulting in stable solid electrolyte interface (SEI) layer and electrode structure. The Li|3D Cu/ZnO/F cell can be stably cycled over 300 cycles with 98% of coulomb efficiency at 0.5 mA cm−2, 1 mAh cm−2. The synergistic effects of both ZnO and fluorine on inducing the uniform deposition of lithium by providing bonding sites can inhibit the generation of lithium dendrites and thus improve the electrochemical performance of lithium metal batteries.

Paraffin wax protecting 3D non-dendritic lithium for backside-plated lithium metal anode

Trapping Li into three-dimensional (3D) conductive host to construct 3D-Li is an effective strategy to suppress the growth of Li dendrites. However, the increased contact area between 3D-Li and electrolyte unavoidably induces more side reactions to further deteriorate the electrochemical performance of lithium metal batteries (LMBs). Herein, we use low-cost paraffin wax (PW) as the conformal protection layer of 3D non-dendritic Li (PW@3D-Li) to improve the cycling stability and safety of LMB via backside plating configuration. During the first charging process, PW overlayer serves as an ionic/electronic insulator to protect 3D-Li from the frontal attack of Li+ ions originating from the cathode, which have to travel over its edge and backside deposit in the interior and bottom of 3D host. During subsequent cycles, the plating and stripping of Li are confined beneath the PW protection layer to mitigate the corrosion of electrolyte and depress the formation of Li dendrites and “dead Li”. Attributing to these advantages, the symmetric PW@3D-Li battery exhibits long cycling life (1050 cycles) and low voltage hysteresis (289 mV at 20 mA cm−2). Additionally, the PW@3D-Li‖Li(Ni1/3Mn1/3Co1/3)O2 battery also exhibits excellent rate capability. Overall, this study offers new fundamental insights for the design of stable and safe LMBs.

A highly stable glass fiber host for lithium metal anode behaving enhanced coulombic efficiency

Lithium metal is the most promising anode for lithium rechargeable batteries due to the extra-high theoretical specific capacity and low electrochemical potential. However, lithium dendrite growth and infinite volume change during reduplicative plating/stripping processes induce the security issue, low coulombic efficiency and poor cycle performance of lithium metal batteries. Here, with high tensile strength, elasticity and good chemical resistance, glass fiber films are employed as a three-dimensional host of lithium metal anode, on which, golden nanoparticles are coated by cool sputtering to direct the planiform deposition of lithium. Thanks to the effective suppression of lithium dendrite growth, a stable and reversible lithium metal anode is achieved with an average coulombic efficiency of 98.1% over 400 cycles in ether-based electrolyte (at a current density of 1 mA cm−2 for a total of 1 mAh cm−2 of lithium). Besides, compared with carbon nanofiber films which the voltage hysteresis increased drastically after 50 cycles, glass fiber films exhibit more stable cyclic performance over 200 cycles. Furthermore, a full battery when it is coupled the anode with lithium iron phosphate shows enhanced rate capability and high cycle stability with retention of 95.6% at 2C over 150 cycles, which demonstrates a promising high-energy and safe rechargeable lithium metal battery.

Enhanced Electrochemical and Safety Performance of Lithium Metal Batteries Enabled by the Atom Layer Deposition on PVDF-HFP Separator

Lithium metal batteries, due to their unique advantages, such as being lightweight and having the lowest anode potential and the highest theoretical specific capacity, have been regarded as a promi...

Silver Nanoparticle-Doped 3D Porous Carbon Nanofibers as Separator Coating for Stable Lithium Metal Anodes.

The ever-increasing demand for electric devices and vehicles prompts the fast development of energy storage systems. Lithium metal is thought to be the most promising electrode for high-performance batteries. However, the growth of lithium dendrites impedes the industrial production of lithium metal batteries. Herein, an effective approach is proposed by coating a commercial separator with three-dimensional porous carbon fibers loaded with silver nanoparticles (Ag-PCNFs), which can be regarded as a subsidiary of the electrode to improve the cycling performance of lithium metal batteries. The porous structure with a high specific surface area endows the electrode with a high lithium-loading capacity. The silver nanoparticles provide the electrode pro-Li property and excellent electrical conductivity, which are beneficial for the electrochemical reaction and reduce the local current density to attain a dendrite-free electrode. Electrochemical cycling performance of symmetric Li-Li batteries shows that Ag-PCNF coating can hinder dendrite growth and enhance the cycling stability, indicating that Ag-PCNFs acting as host materials can effectively guide the deposition of Li and solve the dendrite problem.

Effect of the dielectric constant of a liquid electrolyte on lithium metal anodes

Lithium metal is considered one of the most promising anode materials for realizing high volumetric and gravimetric energy density, owing to the high specific capacity (∼3860 mAh g−1) and the low electrochemical potential of lithium (−3.04 V vs. the standard hydrogen electrode). However, undesirable dendritic lithium growth and corresponding instability of the solid electrolyte interphase prevent safe and long-term use of lithium metal anodes. This paper presents a simple electrolyte approach to enhance the performance of lithium metal batteries by tuning the dielectric constant of the liquid electrolyte. Electrolyte formulations are designed by changing the concentration of ethylene carbonate to have various dielectric constants. This study confirms that high ethylene carbonate content in a liquid electrolyte enhances the cycling performance of lithium metal batteries because the electric field intensity applied to the electrolyte is reduced in relation to the polarization of the electrolyte and thus allows smooth lithium plating and formation of a stable solid electrolyte interphase. We believe that this approach provides an important concept for electrolyte system design suitable to lithium metal batteries.

Sandwich-structured nano/micro fiber-based separators for lithium metal batteries

Although the increased need for high-energy/power-density energy storage systems has revived the research on lithium metal batteries (LMBs), the influence of the separator on the performance of LMBs is still generally neglected. In the present study, a sandwich-structured separator (referred to as the CGC separator below) composed of two 2.5 µm thick cellulose nanofiber (CNF) surface layers and an intermediate 15 µm thick glass microfiber (GMF) and CNF composite layer is described. While the CNF surface layers of the CGC separator feature a homogeneous distribution of nano-sized pores favoring the attainment of a homogeneous current distribution at both electrodes, the intermediate GMF/CNF layer contains macropores facilitating the ionic transport through the separator. The CGC separator exhibited a much better electrolyte wettability and thermal stability compared to a Celgard separator, due to the use of the hydrophilic and thermally stable CNFs and GMFs. It is also shown that the combination of nano-sized and micro-sized fibers used in the CGC separator yields a higher ionic conductivity than that for the commercial separator (1.14 vs. 0.49 mS cm−1). Moreover, the influence of the separator pore structure (e.g. the porosity and pore distribution) on the performance of LMBs is studied for both Li anodes and LiFePO4 composite cathodes. The results demonstrate that the use of separators with high porosities and homogeneous surface pore distributions can improve the performances (e.g. capacities and stabilities) of LMBs considerably, and also highlights the importance of proper separator/electrode interactions. The present approach constitutes a practical engineering strategy for the production of separators with nano/micro fibers and a promising route for the development of LMBs with improved safety and enhanced electrochemical performances.

High-Efficiency Lithium Metal Batteries with Fire-Retardant Electrolytes

Summary Rechargeable lithium metal batteries are regarded as the holy grail of energy storage systems, but their practical applications have long been hindered by poor cyclability and severe safety concerns. In this work, we report a fire-retardant localized high-concentration electrolyte consisting of 1.2 M lithium bis(fluorosulfonyl)imide in a mixture of flame-retardant triethyl phosphate/bis(2,2,2-trifluoroethyl) ether (1:3 by mol) for 4-V class lithium metal batteries. This electrolyte enables stable, dendrite-free cycling of lithium metal anodes with high Coulombic efficiency of up to 99.2%. Moreover, it exhibits excellent anodic stability even up to 5.0 V and greatly enhances the cycling performance of lithium metal batteries. A Li||LiNi0.6Mn0.2Co0.2O2 battery using this electrolyte can retain >97% capacity after 600 cycles at 1 C rate (ca. 1.6 mA cm−2), corresponding to a negligible capacity decay of

Chemically polished lithium metal anode for high energy lithium metal batteries

The formation of lithium dendrites during operation is a major issue that has prevented the practical application of lithium metal anode, which is considered one of the most promising anode materials for next generation lithium batteries. The formation of dendrites has been attributed to the non-uniform and locally high current densities resulting from the uneven dissolution and deposition of lithium, which is associated with the topographical and electrical inhomogeneity on lithium foil. Herein, we demonstrate a facile chemical polishing strategy to remove the pristine film on lithium foil to simplify the surface chemistry of lithium and enable uniform lithium deposition/dissolution during cycles, which can then effectively improve the electrochemical performance of lithium metal batteries.

Effect of Formation Rates on Performance of Lithium Metal Batteries

Lithium metal rechargeable batteries (LRBs) have the potential to meet the 500 Wh·kg-1 energy density goal set by the US Department of Energy for high energy density batteries [1]. However, two issues need to be addressed in these batteries before their widespread commercialization: (1) safety concerns arising from dendritic growth and (2) limited cycle life due to low Coulombic efficiency and loss of active Li. Since organic solvents are thermodynamically unstable in the presence of highly-reducing Li, significant side reactions take place, the products of which form a solid electrolyte interphase (SEI) on the Li surface. During the production process, Li-ion batteries undergo formation cycling to form a stable SEI and to evaluate the condition of the cell. However, the advantages of early cycle conditioning or formation are not well understood for LRBs, because new SEI forms on the Li surface during each cycle. The present study was undertaken to better understand how early cycling impacts interfacial processes in LRBs and ultimately how variation in the initial cycles impacts the life of the battery. Cycling conditions, which include both charging (deposition) and discharging (stripping), affects the Li anode morphology [2, 3]. Build-up of a stable SEI layer and formation of a uniform Li surface during initial cycling of LRBs helps limit dendritic growth, and cell impedance in subsequent cycling. A stable initial SEI is also necessary to prevent corrosion of the Li metal electrode and to prolong the cycle and calendar life of the cells by limiting side reactions with the new Li surface. Using a high-Ni NMC cathode and a Li metal anode, an assortment of different cycling conditions which impact the dynamics of the Li-electrolyte interface were investigated. Performance was characterized with electrochemical diagnostic tools and surface morphology analysis. Both the deposition and stripping rate affected the impedance of the cell, surface kinetics, and interfacial mass transport, all of which impact the cycle life of LRBs.