Mossy Lithium Research Articles

(Invited) Visualizing Electrode Assembly Movement and Lithiation Gradients in Lithium-Metal Batteries

In this presentation we will introduce dilatometry and profilometry using Operando Energy Dispersive X-Ray Diffraction conducted at the Advanced Photon Source, Argonne National Laboratory. This approach is applied to a Li metal battery with a high-voltage NMC811 cathode but the method is suitable for any and all materials and electrodes.In the technique, micrometer-wide collimated X-rays traverse the electrode assembly, and the Bragg peaks from different crystalline phases are used to track the hard edges of the solid materials as they move due to volume changes in the cell. We visualize, with submicron resolution, the movement of the oxide cathode and microporous separator: the latter is observed through the diffraction of X-rays off the lamellae in the polymer matrix. One can map movement of the cathode and also compression in the porous separator – a task that is beyond the capabilities of mechanical dilatometers. We use our approach to show periodic expansion and contraction of metallic lithium during delithiation and relithiation of the cathode and to quantify formation of mossy lithium on the metal surface. The method is universal, easy to implement in-operando, and is selective in distinguishing between different phases in materials.Another dividend of this method is that it allows the profiling of lithiation gradients in the layered-oxide cathode. In our NMC811/Li cells, the cathode gradients are seen even with weak currents, they occur only during relithiation of the cathode, and they persist as the currents abate during constant-voltage discharge.Other particulars of our experimental approach and observations will also be discussed during the talk.Acknowledgement: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Lithium Dendrite Propagation in Anode-Free Lithium Metal Batteries: An in-Operando Scanning Electron Microscopic Study

In the current technological landscape, lithium metal batteries have significantly surpassed the energy density of conventional lithium-ion batteries. Therefore, The advent of anode-free lithium metal batteries (AFLMBs) offers higher energy densities.. They also provide advantages such as reduced process complexity and lower costs due to their design that eliminates the need for anode materials. Unlike the lithium-ion insertion and extraction reactions in traditional lithium-ion batteries. This makes them easier to lithium dendrite formation, which can puncture the separator or solid electrolytes, among other issues. In this work, we developed anin-operando electron microscopic technique with a unique vacuum square-cell design to ensure air-tight transfer of in-operandocells with vacuum protection into the SEM chamber. We significantly improved the imaging resolution with a windowless design, enabling the direct electron beam to focus on the electrode interfaces. Thus, real-time imaging of Li growth could be achieved via a stable current supply and controlled temperature. we systematically analyzed the Li growth and dendrite propagation behavior in AFLMBs using solid polymer electrolyte (SPE). In particular, we used polyethylene oxide (PEO)-based SPEs containing different lithium salts, namely 25wt% Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Lithium difluoro (oxalateo)borate (LiDFOB), and Lithium bis(oxalate)borate (LiBOB), within a LiFePO4||Cu anode-free cell configuration. Under a fixed current density, Li deposition and stripping were conducted, in which the PEO-LiTFSI SPE exhibited uniform deposition with a mossy lithium dendrite morphology. In the subsequent deposition process, some branching lithium dendrites were observed. Meanwhile, PEO-LiBOB showed uneven Li deposition with needle-like dendritic formation, potentially disrupting the SPE/electrode interface and leading to safety hazards. Lastly, PEO-LiDFOB initially showed mossy lithium deposition. In contrast, a few dendritic lithium structures appeared as the deposition process continued into the intermediate and later stages. The study successfully established a novel in-situ electron microscopy observation platform isolating water and oxygen. This platform recreated the actual battery operating environment, enhancing the credibility of experimental results. Additionally, we successfully elucidated the growth mechanisms of lithium dendrites in SPE with different lithium salts in the LFP||Cu configuration. This in-situ microscope technology aims to observe the relevant mechanisms behind dynamic deposition. Understanding how this deposition affects battery performance and safety and combining it with advanced operational and ex-situ characterization techniques can further promote the development of all-solid -state batteries in the future.

Influence of inhomogeneity of lithium-ion transport within the anode/electrolyte interface on mossy lithium formation

The lithium dendrite issue greatly hinders the development of high-energy-density batteries using lithium metal as the anode. Many attempts over the past decades have been made to resolve the lithium dendrite formation. Whereas the root-growing lithium whiskers at the low deposition rate regime and the fractal lithium dendrite at the high deposition rate regime are well investigated, the growth of mossy dendrites at normal charge conditions is not fully understood so far. This work proposes a phase-field method for simulating the mossy dendrite formation. By taking into account two kinds of lithium-ion migration behaviors in the solid electrolyte interphase (SEI), the fast migration pathway at the fractured SEI versus the slow migration pathway at the intact SEI, our simulation results reveal that the inhomogeneity of lithium-ion migration mechanism within the anode/electrolyte interface is the key to the formation of mossy lithium dendrites.

Unraveling the Influence of Li+‐cation and TFSI−‐anion in Poly(ionic liquid) Binders for Lithium‐Metal Batteries

AbstractIon transport in composite electrodes plays a key role in the electrochemical performance of lithium‐metal batteries (LMBs), particularly at high current densities, and hence, some works have suggested the use of ionic conducting polymers as binders. Herein, in order to assess the importance of the type of ion conduction in binders, two poly(ionic liquid) polymers were analyzed as binders in LiFePO4 (LFP) cathodes: poly(lithium 1‐[3‐(methacryloyloxy)propylsulfonyl]‐1‐(trifluoromethane sulfonyl) imide) (PMTFSI−Li), and poly(diallyldimethylammonium bis(trifluoromethane sulfonyl)imide) (PDADMA−TFSI). Their functionalities allow modulating the individual transport of their counter‐ions, Li+ and TFSI−, respectively; in comparison with conventional PVDF binder. Thus, LFP−C‐Binder cathodes, namely C−PVDF, C−PDADMA−TFSI and C−PMTFSI−Li, were evaluated in LMBs. C−PMTFSI−Li exhibited the best performance reaching the theoretical specific capacity (170.3±0.8 mAh g−1) at C/10, an outstanding capacity at 10 C (100.6±0.5 mAh g−1), and long lifespan (>500 cycles at 1 C). C−PDADMA−TFSI showed good long‐term cycling and high performance at high C‐rate, while C−PVDF ended up fading before reaching 500 cycles. Surprisingly, it was observed that the presence of ionic binders into the cathode formulation influenced on Li0 metal deposition morphology, leading to a more homogeneous plating (specially PMTFSI−Li) in comparison with PVDF; and therefore, exhibiting a mitigation of mossy lithium growth.

Lithium Trithiocarbonate as a Dual‐Function Electrode Material for High‐Performance Lithium–Sulfur Batteries

AbstractThe development of practical lithium–sulfur (Li–S) batteries with prolonged cycle life and high Coulombic efficiency is limited by both parasitic reactions from dissolved polysulfides and mossy lithium deposition. To address these challenges, here lithium trithiocarbonate (Li2CS3)‐coated lithium sulfide (Li2S) is employed as a dual‐function cathode material to improve the cycling performance of Li–S batteries. Interestingly, at the cathode, Li2CS3 forms an oligomer‐structured layer on the surface to suppress polysulfide shuttle. The presence of Li2CS3 alters the conventional sulfur reaction pathway, which is supported by material characterization and density functional theory calculation. At the anode, a stable in situ solid electrolyte interphase layer with a lower Li‐ion diffusion barrier is formed on the Li‐metal surface to engender enhanced lithium plating/stripping performance upon cycling. Consequently, the obtained anode‐free full cells with Li2CS3 exhibit a superior capacity retention of 51% over 125 cycles, whereas conventional Li2S cells retain only 26%. This study demonstrates that Li2CS3 inclusion is an efficient strategy for designing high‐energy‐density Li–S batteries with extended cycle life.

Influence of Inhomogeneity of Lithium-Ion Transport within the Anode/Electrolyte Interface on Mossy Lithium Formation

Influence of Inhomogeneity of Lithium-Ion Transport within the Anode/Electrolyte Interface on Mossy Lithium Formation

3D Detection of Lithiation and Lithium Plating in Graphite Anodes during Fast Charging.

A barrier to the widespread adoption of electric vehicles is enabling fast charging lithium-ion batteries. At normal charging rates, lithium ions intercalate into the graphite electrode. At high charging rates, lithiation is inhomogeneous, and metallic lithium can plate on the graphite particles, reducing capacity and causing safety concerns. We have built a cell for conducting high-resolution in situ X-ray microtomography experiments to quantify three-dimensional lithiation inhomogeneity and lithium plating. Our studies reveal an unexpected correlation between these two phenomena. During fast charging, a layer of mossy lithium metal plates at the graphite electrode-separator interface. The transport bottlenecks resulting from this layer lead to underlithiated graphite particles well-removed from the separator, near the current collector. These underlithiated particles lie directly underneath the mossy lithium, suggesting that lithium plating inhibits further lithiation of the underlying electrode.

A core@sheath nanofiber separator with combined hardness and softness for lithium-metal batteries

Lithium metal shows great promise to be the anode material of next-generation electrical energy storage, but the uncontrollable growth of dendritic and mossy lithium greatly restricts the practical application of lithium-metal batteries. Herein, we demonstrate a sustainable strategy for creating a core-shell structured polyimide@fluorinated poly-m-phenyleneisophthalamide (PI@F-PMIA) nanofiber separator coupled hardness with softness via coaxial electrospinning technique. The PI core with good heat-resistance and breaking tenacity acts as a steady and powerful skeleton support to guarantee the structural stability of the PI@F-PMIA separator, even in the wet environment of the working battery. Meanwhile, the gel F-PMIA shell can endow the PI@F-PMIA membrane with a more intimate electrolyte contact to further enhance the electrolyte affinity so as to improve the ion transport capacity. Therefore, the as-prepared PI@F-PMIA nanofiber membrane delivers the synchronous characteristics of the favorable wetting mechanical flexibility, laudable thermal stability, excellent electrolyte uptake as well as distinct gelation phase, which has the capability to overcome the obstacle of lithium dendrites growth and enable a homogeneous stable electrolyte interface. As a result, the good ionic conductivity and interfacial compatibility can be obtained by using the functionalized PI@F-PMIA separator, and the voltage of the relevant lithium symmetrical battery delivers the relatively minor change during 350 h at 2.0 mA·cm−2. More importantly, the as-assembled PI@F-PMIA-based lithium-metal cells present superior cycling stability with the capacity retention of 83.1% and Coulombic efficiency of 99.7% after 200 cycles at 0.5 C rate, accompanied by an excellent rate recovery capability. It follows that the newfangled PI@F-PMIA nanofiber membrane with softness and strength can be perceived to be a highly qualified separator for high-safety and dendrite-proof lithium-metal batteries.

Structure and mechanical properties of electroplated mossy lithium: Effects of current density and electrolyte

Mechanical suppression, e.g., by applying stack pressures and using functionalized coatings, has been considered a promising approach to inhibit the formation of lithium (Li) dendrites and improve the cycling stability of the Li metal electrode. However, a lack of understanding of the mechanical behavior of electroplated mossy Li, consisting of loosely packed Li dendrites that are covered by solid electrolyte interphase, hinders the development of mechanical suppression strategies and limits the understanding of the electromechanical behavior of mossy Li. In this study, we investigated, using flat punch indentation in an argon-filled glovebox, the room temperature mechanical behavior and its relationship with the microstructure of mossy Li electroplated using different current densities (between 0.25 and 10 ​mA/cm2) in several electrolytes. The dendrite size decreases and the porosity of mossy Li increases with increasing current density. Mossy Li has lower Young’s modulus (E) but significantly higher creep resistance than bulk Li. A scaling relationship between E and porosity is established for mossy Li. The creep behavior of mossy Li exhibits a strong size effect, i.e., the steady-state impression velocity decreases with decreasing dendrite size. These findings provide a comprehensive understanding of the relationship between the microstructure and mechanical behavior of mossy Li.

(Invited) Keeping It Simple: Anode Free Lithium Metal Cells with Liquid Electrolytes As a Path to Higher Energy Density

In the pursuit of higher energy density, both academia and industry are intensely researching many alternative rechargeable battery concepts beyond conventional lithium-ion cells. The most promising alternatives will be those that can achieve cell level energy density larger than that of state-of-the-art lithium ion batteries at a comparable or lower cost. Based on these criteria, anode free lithium metal cells emerge as potentially useful lithium-ion alternatives as their simple cell construction can enable both high energy density and low cost assembly. In anode free cells, the negative electrode begins as a bare copper current collector and the lithium metal anode is plated in-situ from the lithium inventory in the cathode. These cells can achieve energy density 40-50% greater than lithium-ion at the cell level and have a simpler cell construction that eliminates the need to handle lithium metal foils or coat active materials on the negative current collector. However, the cycling stability of these cells in conventional carbonate liquid electrolytes is often terrible due to the low CE of lithium metal and the lack of an excess lithium reservoir. In this way, anode free cells exaggerate the technical challenges of lithium metal which makes them excellent test vehicles for optimizing lithium metal cycling. In this presentation we will highlight our progress in improving lithium metal cycling efficiency in liquid electrolytes toward the development of safe, practical, high energy density anode free cells. Much of this work focuses on the development and characterization of anode free LiNi0.5Mn0.3Co0.2O2 (NMC 532)//Cu wound pouch cells. We demonstrate that the cycling stability and safety of these cells is directly correlated to the morphology of the lithium plated during charge. High surface area mossy lithium deposits in conventional liquid electrolytes lead to fast capacity fade and high anode reactivity. We will also show how many different factors including, cycling rate, charge protocol, applied pressure, temperature, and electrolyte composition affect lithium morphology. Our latest results will be highlighted which show that with the appropriate electrolyte chemistry and cycling conditions, smooth lithium morphology with densely packed columns 50 um in diameter can be achieved after cycling in liquid electrolytes. This excellent lithium morphology significantly improves the capacity retention (Figure 1) of anode free cells and limits the reactivity of the deposited lithium. Cell failure mechanisms will also be addressed with insight as to how these failures can be overcome to further improve cycle life. These results demonstrates that stable cycling of dendrite free lithium metal is possible in simple anode free cells with liquid electrolytes which represents a promising and practical avenue for the design of high energy density batteries. Figure 1

Mechanical behavior of electroplated mossy lithium at room temperature studied by flat punch indentation

We report the Young's modulus and deformation behavior of electroplated mossy lithium at room temperature investigated by flat punch indentation inside an argon-filled glovebox. The Young's modulus of the mossy lithium with a porosity of about 62.3% is measured to be about 2 GPa, which is smaller than that (∼7.8 GPa) of bulk lithium. Both the mossy and bulk lithium show clearly an indentation creep behavior. Despite its highly porous microstructure, the impression creep velocity of the mossy lithium is less than one-thirtieth of that of bulk lithium under the same stress. We proposed possible mechanisms for the significantly higher deformation and creep resistance of the mossy lithium over bulk lithium. These findings are key to developing mechanical suppression approaches to improve the cycling stability of lithium metal electrodes.

Composite Lithium Metal Anode Via a Simple Rolling-Cutting Method

Lithium metal–based batteries are attractive energy storage devices because of high energy density. However, uncontrolled dendrite growth and virtually infinite volume change, which cause performance fading and safety concerns, have limited their applications. Here, we demonstrate that a composite lithium metal electrode with an ion-conducting mesoscale skeleton can improve electrochemical performance by locally reducing the current density. In addition, the potential for short-circuiting is largely alleviated due to side deposition of mossy lithium on the three-dimensional electroactive surface of the composite electrode. Moreover, the electrode volume only slightly changes with the support of a rigid and stable scaffold. Therefore, this mesoscale composite electrode can cycle stably for 200 cycles with low polarization under a high areal current density up to 5 mA/cm2. Most attractively, the proposed fabrication process, which only involves simple mechanical deformation, is scalable and cost effective, providing a new strategy for developing high performance and long lifespan lithium anodes. It is worth noting that this composite electrode design holds great promise for metal electrodes coupled with solid electrolyte. Figure 1

Composite lithium electrode with mesoscale skeleton via simple mechanical deformation

Lithium metal-based batteries are attractive energy storage devices because of high energy density. However, uncontrolled dendrite growth and virtually infinite volume change, which cause performance fading and safety concerns, have limited their applications. Here, we demonstrate that a composite lithium metal electrode with an ion-conducting mesoscale skeleton can improve electrochemical performance by locally reducing the current density. In addition, the potential for short-circuiting is largely alleviated due to side deposition of mossy lithium on the three-dimensional electroactive surface of the composite electrode. Moreover, the electrode volume only slightly changes with the support of a rigid and stable scaffold. Therefore, this mesoscale composite electrode can cycle stably for 200 cycles with low polarization under a high areal current density up to 5 mA/cm2. Most attractively, the proposed fabrication process, which only involves simple mechanical deformation, is scalable and cost effective, providing a new strategy for developing high performance and long lifespan lithium anodes.

Influence of Low-Temperature Charge on the Mechanical Integrity Behavior of 18650 Lithium-Ion Battery Cells Subject to Lateral Compression

The study on the damage tolerance and failure mechanism of lithium-ion batteries (LIBs) subject to mechanical attack has attracted considerable attention. The electrochemical performance and thermal behavior of LIB were significantly affected by operation temperature and charging rate, but the dependence of these two factors on mechanical response remains unclear. Hence, we investigated how the environmental temperatures and rates in charging process affected the mechanical response characteristics of 18650 LIB cells. The onset of the short circuit in the cells which charged at temperatures above −25 °C occurred around their modulus peak under compression. At −25 °C, there was a strong possibility that a premature short circuit occurred locally in the cells during charging, thus they might show complex and variable mechanical response under compression. The failure moduli and crushing stresses of cells subject to compression tended to decrease as their ambient charging temperatures went down. Besides, 0.5 C-charged cells exhibited higher failure moduli and crushing stresses than the 1 C-charged cells above −20 °C. Morphology analyses of the cell electrode surfaces revealed that mossy lithium deposits became evident at temperatures below −10 °C. Furthermore, their distribution was uniform. Mechanical results also indicated that the short-term cycling at −20 °C and 0.5 C would soften the cell.

Uniform Lithium Nucleation Guided by Atomically Dispersed Lithiophilic CoNx Sites for Safe Lithium Metal Batteries

AbstractThe mossy lithium dendrite growth during repeated lithium plating/stripping induces low Coulombic efficiency, poor lifespan, and safety concerns of working lithium metal batteries. Herein, atomically dispersed CoNx‐doped graphene is exploited as a host to accommodate dendrite‐free lithium deposits. The coordination between Co and N in the conductive matrix can effectively regulate the local electronic structure, and thereby enhance the adsorption of lithium ions and promote the following nucleation process. Meanwhile, the doped N facilitates high dispersion of Co atoms into graphene through the CoN coordination bond. The strong lithiophilicity provided by N coordinated with Co promises a uniform lithium nucleation behavior, further contributing to the smooth lithium deposition morphology. These characteristics afford a superhigh Coulombic efficiency of 99.2% at 2.0 mA cm−2 (≈400 cycles) and 5.0 mA cm−2 (350 cycles), and 98.2% at 10.0 mA cm−2 (200 cycles) with a capacity of 2.0 mAh cm−2. LiFePO4|CoNC–Li full cells deliver a long lifespan of 340 cycles at 1.0 C (240 cycles for routine cells). This offers fresh insights into effectively regulating the lithiophilic chemistry of lithium metal host toward uniform nucleation and growth of lithium deposits in working high‐energy‐density batteries.

Lithiophilic-lithiophobic gradient interfacial layer for a highly stable lithium metal anode

The long-standing issue of lithium dendrite growth during repeated deposition or dissolution processes hinders the practical use of lithium-metal anodes for high-energy density batteries. Here, we demonstrate a promising lithiophilic–lithiophobic gradient interfacial layer strategy in which the bottom lithiophilic zinc oxide/carbon nanotube sublayer tightly anchors the whole layer onto the lithium foil, facilitating the formation of a stable solid electrolyte interphase, and prevents the formation of an intermediate mossy lithium corrosion layer. Together with the top lithiophobic carbon nanotube sublayer, this gradient interfacial layer can effectively suppress dendrite growth and ensure ultralong-term stable lithium stripping/plating. This strategy is further demonstrated to provide substantially improved cycle performance in copper current collector, 10 cm2 pouch cell and lithium–sulfur batteries, which, coupled with a simple fabrication process and wide applicability in various materials for lithium-metal protection, makes the lithiophilic–lithiophobic gradient interfacial layer a favored strategy for next-generation lithium-metal batteries.

In-Situ AFM Measurements on Lithium Metal Anodes

Using lithium metal electrode for the next generation of Lithium Ion Batteries (LIB) possesses the advantage of high energy around 300 Wh/kg coupled with progressed cathode material [1]. However, the formation of lithium dendrites and mossy lithium under electrochemical load (cycling) are currently the major hindrance of a wider use of such material and commercialization of the concept. Recently, the aforementioned challenges have been analyzed by means of nuclear magnetic resonance and found [2]. Those formations lead to degradation processes which are not yet understood at the micro- and nanometer scale. Therefore, experiments with high spatial resolution under realistic conditions gaining a better understanding of such phenomena are of utmost importance. Based on the practical significance for various applications the in-situ atomic force microscopy (AFM) characterization under electrochemical load is a key to develop new devices with improved functionality. Within this contribution we present combined atomic force microscopy and cyclic voltammetry (CV) measurements of the electrode-electrolyte interface between lithium anode and LP 30 (LiPF6 in EC/DMC), a common electrolyte in conventional energy storage. Therefore, the simultaneous investigation of structural, electrochemical and mechanical properties under electrochemical conditions is demonstrated. We will discuss the formation of mossy lithium as well as the formation of dendrites within the in-situ AFM results. Our results shed light onto the small scale processes on lithium metal anodes for LIBs and path the way towards applicability of bare lithium as anode material.

Lithium metal protection enabled by in-situ olefin polymerization for high-performance secondary lithium sulfur batteries

Lithium metal is considered to be the optimal choice of next-generation anode materials due to its ultrahigh theoretical capacity and the lowest redox potential. However, the growth of dendritic and mossy lithium for rechargeable Li metal batteries lead to the possible short circuiting and subsequently serious safety issues during charge/discharge cycles. For the further practical applications of Li anode, here we report a facile method for fabricating robust interfacial layer via in-situ olefin polymerization. The resulting polymer layer effectively suppresses the formation of Li dendrites and enables the long-term operation of Li metal batteries. Using Li-S cells as a test system, we also demonstrate an improved capacity retention with the protection of tetramethylethylene-polymer. Our results indicate that this method could be a promising strategy to tackle the intrinsic problems of lithium metal anodes and promote the development of Li metal batteries.

Visualization of Lithium Plating and Stripping via in Operando Transmission X-ray Microscopy

Lithium dendrite growth dynamics on Cu surface is first visualized through a versatile and facile experimental cell by in operando transmission X-ray microscopy (TXM). Galvanostatic plating and stripping cycle(s) are applied on each cell. Upon plating/stripping at ∼1 mA cm–2, mossy lithium is clearly found growing and shrinking on the Cu surface as the application time increases. It is interesting to note that the aspect ratio (height/width) of deposited lithium has increased with charge passed during plating, indicating a faster growing from the base. In addition, the dendritic or mossy lithium has also been observed when various high current densities (25, 12.5, and 6.3 mA cm–2) are applied in different cycles, showing a severe dendritic lithium formation that could be induced by inhomogeneous current distribution. The clear structure of dead lithium is found after the cycling, which also shows a lower efficiency and higher hazard when a higher current density is applied. This work explores TXM as a use...

A nanoindentation study of the viscoplastic behavior of pure lithium

Applying mechanical stresses is a possible approach to suppress dendrite and mossy lithium (Li) in Li metal electrodes. We conducted, in this work, nanoindentation tests on pure Li metal in an argon-filled glove box to study its viscoplastic behavior at room temperature. Both load-controlled and strain rate-controlled nanoindentations showed clear viscoplastic characteristics of Li. Based on an iterative finite element (FE) modeling approach, we determined a viscoplastic constitutive law for Li. In addition, we demonstrated by FE modeling that elastic modulus, on the order of GPas, has a negligible influence on the nanoindentation response of Li at ambient temperature.