Lithium Metal Electrode Research Articles

Kinetics of lithium electrodeposition and stripping.

Electrodeposition and stripping are fundamental electrochemical processes for metals and have gained importance in rechargeable Li-ion batteries due to lithium metal electrodes. The electrode kinetics associated with lithium metal electrodeposition and stripping is crucial in determining the performance at fast discharge and charge, which is important for electric vertical takeoff and landing (eVTOL) aircraft and electric vehicles (EV). In this work, we show the use of Marcus-Hush-Chidsey (MHC) kinetics to accurately predict the Tafel curve data from the work of Boyle et al. [ACS Energy Lett. 5(3), 701 (2020)]. We discuss the differences in predictions of reorganization energies from the Marcus-Hush and the MHC models for lithium metal electrodes in four solvents. The MHC kinetic model is implemented and open-sourced within Cantera. Using the reaction kinetic model in a pseudo-2D battery model with a lithium anode paired with a LiFePO4 cathode, we show the importance of accounting for the MHC kinetics and compare it to the use of Butler-Volmer and Marcus-Hush kinetic models. We find significant deviation in the limiting currents associated with reaction kinetics for the three different rate laws for conditions of fast charge and discharge relevant for eVTOL and EV, respectively.

New High Donor Electrolyte for Lithium-Sulfur Batteries.

The unparalleled theoretical specific energy of lithium-sulfur (Li-S) batteries has attracted considerable research interest from within the battery community. However, most of the long cycling results attained thus far relies on using a large amount of electrolyte in the cell, which adversely affects the specific energy of Li-S batteries. This shortcoming originates from the low solubility of polysulfides in the electrolyte. Here, 1,3-dimethyl-2-imidazolidinone (DMI) is reported as a new high donor electrolyte for Li-S batteries. The high solubility of polysulfides in DMI and its activation of a new reaction route, which engages the sulfur radical (S3 •- ), enables the efficient utilization of sulfur as reflected in the specific capacity of 1595mAhg-1 under lean electrolyte conditions of 5 μLelectrolyte mgsulfur -1 . Moreover, the addition of LiNO3 stabilizes the lithium metal interface, thereby elevating the cycling performance to one of the highest known for high donor electrolytes in Li-S cells. These engineered high donor electrolytes are expected to advance Li-S batteries to cover a wide range of practical applications, particularly by incorporating established strategies to realize the reversibility of lithium metal electrodes.

Application of magnetron sputtering to deposit a multicomponent separator with polysulfide chemisorption and electrode stabilization for high-performance lithium‑sulfur batteries

Lithium‑sulfur battery has attracted immense attention because of its extraordinary high energy density and theoretical capacity. However, its practical application has been seriously hindered by the rapid capacity degradation associated with the “shuttle effect” and unstable electrodes. Such negative issues during charge-discharge process could be alleviated by modification of the separator, which is demonstrated in this paper. Here, we report a sandwich-type vanadium nitride/polyvinylidene fluoride-polymethylmethacrylate/hexagonal boron nitride separator (VN/PVDF-PMMA/hBN) by electrospinning of PVDF-PMMA nanofiber membrane, followed by magnetron sputtering of VN and hBN layer at the opposite size of the membrane. Compared to conventional coating method, magnetron sputtering led to an ultrathin coating layer of 200 nm. The sputtered VN/PVDF-PMMA/hBN separator showed higher porosity (68.7%) than commercial polypropylene (PP) separator (44.5%), and significantly high electrolyte uptake (335.8% s. 175.9%), which can lead to rapid transportation of lithium ions. In the meantime, the membrane showed clear benefit in inhibiting polysulfide diffusion and lithium metal electrode stabilization due to the presence of polar CO groups that interact with the polysulfides. As a result, the LiS battery with VN/PVDF-PMMA/hBN separator showed a high initial discharge capacity of 1077.4 mAh g−1 at 0.2C, which only slightly decreased to 905.1 mAh g−1 after 200 cycles. Significantly higher than the battery with commercial PP separator.

Propylene carbonate-nitrile solvent blends for thermally stable gel polymer lithium ion battery electrolytes

Gel polymer electrolytes (GPEs) based on poly (vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP) containing propylene carbonate (PC), isobutyronitrile (IBN) and trimethyl acetonitrile (TMAN) solvent blend electrolytes were developed to enhance high temperature electrochemical performance and to improve safety of LiNi3/5Mn1/5Co1/5O2 (NMC622)‖graphite lithium ion battery (LIB) cells. These liquid electrolytes (LE) consist of lithium bis(trifluoro-methane)sulfonimide (LiTFSI) as conducting lithium salt and PC/nitrile (1:1, v/v) solvent blends. Ethylene sulfite (ES) and vinylene carbonate (VC) were used as solid electrolyte interphase (SEI) forming additives and contributing to an excellent cycling stability of electrolytes comprising nitrile solvents in NMC622‖graphite cells. Electrochemical impedance spectroscopy (EIS), pulsed field gradient nuclear magnetic resonance spectroscopy (PFG NMR) and relative permittivity determination reveal remarkable ion conducting properties of IBN and TMAN solvents. Since their electrolytes are incompatible with lithium metal electrodes, their electrochemical stability window (ESW) was determined using lithiated lithium titanate (Li7Ti5O12) (LTO) as counter and reference electrodes and the obtained values were confirmed by quantum mechanical computation. Differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) confirmed significantly improved safety of IBN and TMAN containing electrolytes. Therefore, PVdF-HFP-based GPEs containing PC/nitrile solvent blends are a promising alternative to SOTA electrolyte for battery cycling at elevated temperature (60 °C) in NMC622‖graphite cells.

Stiffer is Not Necessarily Better: Requirements Analysis for Binary Solid Polymer Electrolytes that Ensure Stable Lithium Metal Electrodes

Use of lithium metal electrodes in solid state batteries requires well-balanced electrochemical and mechanical properties for high performance yet safe application. We present a new methodology to account for coupling mechanisms between electrochemistry and mechanics, understand morphological stability and deduce stability maps for solid polymer electrolytes adjacent to metal electrodes. We use a rigorous electro-chemo-mechanical description of the polymer electrolyte and its reaction kinetics to predict the interface current density along a deformed electrolyte interface as a function of e.g. mechanical stiffness, transport and interface properties. With these results, we explore the stability of the electrolyte-electrode interface in regard to the tendency for protrusions to grow on the metal electrode. We find that there is a critical Young’s modulus of the electrolyte above which protrusion growth is suppressed. However, the critical Young’s modulus depends on the charging rate, and on the electrochemical transport properties of the electrolyte and the interface. We develop a morphological stability map in which the critical Young’s modulus separating stable and unstable behavior is identified. The results agree well with experimental findings and might help in predicting new classes of polymer electrolytes which are more likely to perform well in the effort to suppress dendrite growth.

Submicron interlayer for stabilizing thin Li metal powder electrode

The surface area of the lithium metal electrode must be considered when attempting to suppress dendritic growth of lithium metal, as surface area can lower the effective current density. For this reason, lithium metal powder (LiMP) has attracted much attention for use in electrodes because of its higher surface area. However, repeated cycling, even in aging time, leads to delamination of lithium particles from flat metal current collectors and results excess dead lithium particles, even in LiMP electrodes. Herein, this problem is addressed by coating submicron-thickness carbon interlayers on copper current collectors for LiMP electrodes. This thin carbon layer plays important roles in both maintaining the interfacial contact between Cu foil and LiMP particles and lowering overpotential in Li/Li symmetric cells, which leads to improve electrochemical performance in thin LiMP (40 μm) based cell. These enhancements are related to the enlarged surface area, as confirmed by higher adhesion of the electrode after precycling. Furthermore, the carbon materials are also believed to contribute to seeding for efficient lithium nucleation. Thus, thin carbon layers on current collectors can provide simple but powerful enhancements to the electrochemical performance of high-energy-density LMSBs.

Bottom-Up Lithium Growth Triggered by Interfacial Activity Gradient on Porous Framework for Lithium-Metal Anode

Three-dimensional (3D) porous frameworks have attracted considerable interest as lithium-metal electrodes for next-generation rechargeable batteries. The high surface areas and large pore volumes o...

Solid Electrolyte Interphase Evolution on Lithium Metal Electrodes Followed by Scanning Electrochemical Microscopy Under Realistic Battery Cycling Current Densities

AbstractInvited for this month's cover picture are the groups of Gunther Wittstock at Carl von Ossietzky University of Oldenburg (Germany) and Martin Winter at Helmholtz‐Institute Münster (Germany). The cover picture shows an artistic vision by Andre Bar of the submerged probe surveying a very reactive solid|liquid interface, such as Li metal electrodes, while reactions are going on. Read the full text of the Article at 10.1002/celc.202000441.

Polymer-Inorganic Nanocomposite Coating with High Ionic Conductivity and Transference Number for a Stable Lithium Metal Anode.

We report a nanocomposite coating for lithium metal protection, which consists of nanosized LiF particles embedded into a PEO polymer matrix. The composite offers a large LiF/PEO interface area throughout the coating, promoting an exceptionally high ionic 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. A full cell with the coated lithium metal anode and an NMC622 cathode with an areal capacity of 1 mA h cm-2 shows much improved specific capacity and cycling stability. The cell exhibits a high initial capacity of 135 mA h g-1 and a capacity retention of 83% 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 mA h g-1 and a capacity retention of 74% after 300 cycles.

Wetting Phenomena and their Effect on the Electrochemical Performance of Surface-Tailored Lithium Metal Electrodes in Contact with Cross-linked Polymeric Electrolytes.

Li metal batteries (LMBs) containing cross‐linked polymer electrolytes (PEs) are auspicious candidates for next‐generation batteries. However, the wetting behavior of PEs on uneven Li metal surfaces has been neglected in most studies. Herein, it is shown that microscale defect sites with curved edges play an important role in a wettability‐dependent electrodeposition. The wettability and the viscoelastic properties of PEs are correlated, and the impact of wettability on the nucleation and diffusion near the Li|PE interface is distinguished. It is found that the curvature of the edges is a key factor for the investigation of wetting phenomena. The appearance of microscale defects and phase separation are identified as main causes for erratic nucleation. It is emphasized that the implementation of stable and consistent long‐term cycling performance of LMBs using PEs requires a deeper understanding of the “soft‐solid”–solid contact between PEs and inherently rough Li metal surfaces.

Performance and behavior of LLZO-based composite polymer electrolyte for lithium metal electrode with high capacity utilization

Abstract A thin membrane (≈47 μm) of a Celgard separator-reinforced cross-linked LiTFSI-PEO-Pyr14TFSI-LLZO composite polymer electrolyte (CgCPE) was prepared and investigated for its ability to suppress the formation and propagation of high surface area lithium (HSAL) with dendritic morphology. The membrane shows superior cycling stability in Li||Li-symmetric cells under high capacity utilization (5 mAh/cm2) for up to 2000 h. Using a combination of conventional laboratory techniques and nondestructive synchrotron X-ray tomography, the synergetic effect of the membrane components towards homogenous lithium electrodeposition/dissolution was revealed. The modulated ion migration in CgCPE and decreased interfacial/interphasial resistance ensures an evenly regulated Li-ion flux during deposition. While, the good mechanical properties of the CgCPE membrane were maintained up to a capacity utilization of 15 mAh/cm2. Based on the results, an approach for a hybrid solid electrolyte to control lithium electrodeposition for Li metal electrodes with high capacity utilization is provided, and furthermore, such an approach could be further used for lithium metal batteries with high energy density and safety.

Evaluation of chemical stability of conducting ceramics to protect metallic lithium in Li/S batteries

Among the different cutting-edge solutions currently under investigation, lithium metal technologies have received a renewed interest. Thorough research work is currently carried out to enhance the safety and cyclability of the lithium metal electrode, targeting high energy post-Li-ion systems such as the lithium/sulfur technology. This study aims at investigating different inorganic protective layers that could be placed at the surface of the lithium metal electrode in a lithium/sulfur system, in order to prevent the detrimental interactions with polysulfide species and electrolyte components. The chemical stability of the selected inorganic materials (amorphous thin films, crystalline ceramics and glass-ceramics) towards ether-based (polysulfides-containing) electrolytes was studied. Although being crucial for long term cycling of Li/S cells, this issue has not been addressed so far. The chemical composition and morphology of the different materials after immersion in different electrolytes were characterized by X-ray diffraction, XPS and SEM, and the most promising materials were evaluated in Li/S cells.

Effect of Urea as Electrolyte Additive for Stabilization of Lithium Metal Electrodes

Owing to its lowest standard redox potential, low density, and high theoretical specific capacity, lithium metal has been considered to be the ideal anode material for secondary lithium batteries. ...

Artificial Solid Electrolyte Interphases for Lithium Metal Electrodes by Wet Processing: The Role of Metal Salt Concentration and Solvent Choice.

In this study, the artificial solid electrolyte interphase (SEI) formed on lithium metal when treated in ZnCl2 solutions is thoroughly investigated. The artificial SEI on lithium metal electrodes substantially decreases the interfacial resistance by ca. 80% and improves cycling stability in comparison to untreated lithium. The presence of a native SEI negatively affects the morphology and interfacial resistance of the artificial SEI. Increasing the ZnCl2 concentration in tetrahydrofuran (THF) (precursor solution) results in higher homogeneity of the surface morphology. Independent of the ZnCl2 concentrations, the artificial SEI is composed of Cx, CO, LiCl, Li2CO3, ZnCl2, and LixZny alloys. ZnCl2 (1 M) produces the most homogenous surface and additional surface species with carbonyl side groups. Nonetheless, the ZnCl2 concentration only has a small effect on the interfacial resistance or cycling stability. Using ethyl methyl carbonate (EMC) as the solvent significantly reduces the interfacial resistance to 7 Ω cm2, in comparison to 25 Ω cm2 for THF. The composition of the artificial SEIs varies depending on the solvent. Either way, the SEI consists of Cx LixC, LiCl, Li2CO3, ZnCl2, and LiZn alloys. The THF-based SEI additionally features ether and carbonyl groups, LiZnO, and Zn metal. For the artificial SEI formed with both solvents, the atomic percentage of the LiZn alloy increases close to the Li surface.

Mapping Li-Ion Transport Through a Ceramic Electrolyte by X-Ray Computed Tomography

Low values of critical-current-densities are a significant shortcoming in the performance of Li6.25La3Zr2A10.25O12, a ceramic electrolyte. X-ray Computed Tomography (CT) images obtained from pristine and exhausted cells constructed with lithium metal electrodes, are used to map the spatial non-uniformity of lithium transport. The current is shown to be concentrated in a limited area of the interface, ostensibly producing low engineering values of the critical-current-density. The total volume of Li-ion transfer calculated from the CT scans, is consistent with Faradaic transport. A qualitative analysis of the maps suggests a current concentration factor of at least ten, and most likely even higher.

The Fast Charge Transfer Kinetics of the Lithium Metal Anode on the Garnet‐Type Solid Electrolyte Li6.25Al0.25La3Zr2O12

AbstractThe charge transfer kinetics between a lithium metal electrode and an inorganic solid electrolyte is of key interest to assess the rate capability of future lithium metal solid state batteries. In an in situ microelectrode study run in a scanning electron microscope, it is demonstrated that—contrary to the prevailing opinion—the intrinsic charge transfer resistance of the Li|Li6.25Al0.25La3Zr2O12 (LLZO) interface is in the order of 10−1 Ω cm2 and thus negligibly small. The corresponding high exchange current density in combination with the single ion transport mechanism (t+ ≈ 1) of the inorganic solid electrolyte enables extremely fast plating kinetics without the occurrence of transport limitations. Local plating rates in the range of several A cm−2 are demonstrated at defect free and chemically clean Li|LLZO interfaces. Practically achievable current densities are limited by lateral growth of lithium along the surface as well as electro‐chemo‐mechanical‐induced fracture of the solid electrolyte. In combination with the lithium vacancy diffusion limitation during electrodissolution, these morphological instabilities are identified as the key fundamental limitations of the lithium metal electrode for solid‐state batteries with inorganic solid electrolytes.

Solid Electrolyte Interphase Evolution on Lithium Metal Electrodes Followed by Scanning Electrochemical Microscopy Under Realistic Battery Cycling Current Densities

AbstractLithium metal electrodes were cycled in 1 M LiClO4 in propylene carbonate with different current densities. The local protecting properties of the solid electrolyte interphase (SEI) were probed by scanning electrochemical microscopy (SECM) in the feedback mode directly within the cell in between charging‐discharging cycles. This was enabled by placing the negative electrode into an in‐house micro‐milled cell with a central opening in the counter electrode for inserting the microelectrode. Finite element simulation of the secondary current distribution proved that the current distribution deviates only slightly in the area of the opening provided that the SECM microelectrode is retracted during the charging‐discharging cycles. The development of lithium deposits was observed by SECM and can be linked to the used charging‐discharging protocol. The Li metal of protruding deposits is significantly more active for electron transfer to the mediator than the remaining parts of the surface. The developed hardware and methodology can be directly applied to other electrolytes or other battery electrodes forming protective films.

A Lithium Metal Anode Surviving Battery Cycling Above 200 °C

Lithium (Li) metal electrode cannot endure elevated temperature (e.g., >200 °C) with the regular battery configuration due to its low melting point (180.5 °C) and high reactivity, which restricts its application in high-temperature Li metal batteries for energy storage and causes safety concerns for regular ambient-temperature Li metal batteries. Herein, this work reports a Li5 B4 /Li composite featuring a 3D Li5 B4 fibrillar framework filled with metallic Li, which maintains its initial structure at 325 °C in Ar atmosphere without leakage of the liquid Li. The capillary force caused by the porous structure of the Li4 B5 fibrillar framework, together with its lithiophilic surface, restricts the leakage of liquid metallic Li and enables good thermal tolerance of the Li5 B4 /Li composite. Thus, it can be facilely operated for rechargeable high-temperature Li metal batteries. Li5 B4 /Li electrodes are coupled with a garnet-type ceramic electrolyte (Li6.5 La3 Zr0.5 Ta1.5 O12 ) to fabricate symmetric cells, which exhibit stable Li stripping/plating behaviors with low overpotential of ≈6 mV at 200 °C using a regular sandwich-type cell configuration. This work affords new insights into realizing a stable Li metal anode for high-temperature Li metal batteries with a simple battery configuration and high safety, which is different from traditional molten-salt Li metal batteries using a pristine metallic Li anode.

Recent Progress in High Donor Electrolytes for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries continue to be considered promising post‐lithium‐ion batteries owing to their high theoretical energy density. In pursuit of a Li–S cell with long‐term cyclability, most studies thus far have relied on using ether‐based electrolytes. However, their limited ability to dissolve polysulfides requires a high electrolyte‐to‐sulfur ratio, which impairs the achievable specific energy. Recently, the battery community found high donor electrolytes to be a potential solution to this shortcoming because their high solubility toward polysulfides enables a cell to operate under lean electrolyte conditions. Despite the increasing number of promising outcomes with high donor electrolytes, a critical hurdle related to stability of the lithium‐metal counter electrode needs to be overcome. This review provides an overview of recent efforts pertaining to high donor electrolytes in Li–S batteries and is intended to raise interest from within the community. Furthermore, based on analogous efforts in the lithium‐air battery field, strategies for protecting the lithium metal electrode are proposed. It is predicted that high donor electrolytes will be elevated to a higher status in the field of Li–S batteries, with the hope that either existing or upcoming strategies will, to a fair extent, mitigate the degradation of the lithium–metal interface.

A universal natural hydroxy propyl methyl cellulose polymer additive for modifying lignocellulose-based gel polymer electrolytes and stabilizing lithium metal anodes

Defects in gel polymer electrolytes (GPEs) limit the comprehensive performance of lithium-ion batteries (LIBs). Even using an excellent lignocellulose (LC)-based GPE is not sufficient for practical applications due to its poor mechanical properties, low liquid absorption and ionic conductivity. To eliminate these limitations, in this work, a novel biodegradable hydroxy propyl methyl cellulose (HPMC) polymer with a remarkable swelling effect was added to an LC-based polymer matrix. The LC/HPMC (LCH) membrane prepared by the phase transfer method retains the excellent performance of the LC membrane. A large amount of free volume is formed in the corresponding GPE due to the swelling effect, which can remarkably improve the physical and electrochemical properties, including the absorption of the liquid electrolyte (1168 wt%), mechanical property (14.45 MPa), ionic conductivity (6.14 × 10−3 S cm−1, 25 °C), lithium ion transfer number (tLi+ = 0.75), charge/discharge performance (162 mA h g−1 at 0.2C), and excellent regulation ability of Li deposition. Moreover, the overpotential of the Li/LCH-based GPE/Li symmetric battery is stable for more than 1000 h, which illustrates that the addition of the HPMC can provide long-term protection for lithium metal electrodes.