Reversible Plating Research Articles

Ultra-high-voltage Ni-rich layered cathodes in practical Li metal batteries enabled by a sulfonamide-based electrolyte

By increasing the charging voltage, a cell specific energy of >400 W h kg−1 is achievable with LiNi0.8Mn0.1Co0.1O2 in Li metal batteries. However, stable cycling of high-nickel cathodes at ultra-high voltages is extremely challenging. Here we report that a rationally designed sulfonamide-based electrolyte enables stable cycling of commercial LiNi0.8Co0.1Mn0.1O2 with a cut-off voltage up to 4.7 V in Li metal batteries. In contrast to commercial carbonate electrolytes, the electrolyte not only suppresses side reactions, stress-corrosion cracking, transition-metal dissolution and impedance growth on the cathode side, but also enables highly reversible Li metal stripping and plating leading to a compact morphology and low pulverization. Our lithium-metal battery delivers a specific capacity >230 mA h g−1 and an average Coulombic efficiency >99.65% over 100 cycles. Even under harsh testing conditions, the 4.7 V lithium-metal battery can retain >88% capacity for 90 cycles, advancing practical lithium-metal batteries.

A Systematic Electrochemical Investigation of a Dimethylamine Cosolvent-Assisted Nonaqueous Zinc(II) Bis(trifluoromethylsulfonyl)imide Electrolyte

The development of the multivalent electrolytes is a critical component to advance polyvalent energy storage technology. In this work, a new and simple nonaqueous zinc electrolyte is developed and investigated where a secondary amine is introduced as a cosolvent. The addition of dimethylamine (DMA) as a cosolvent in THF facilitates the solubilization of Zinc (II) bis(trifluoromethanesulfonyl)imde (Zn(TFSI)2) and results in a homogeneous electrolyte with reversible plating of zinc achieved at high coulombic efficiencies. The electrochemical properties of the developed electrolyte and the effects of the cosolvent and salt concentrations are systematically investigated. It was found that increasing the ratio of the cosolvent DMA in THF for a Zn(TFSI)2 electrolyte leads to more facile kinetics, better ion solubilization, and higher ion mobility evidenced by up a significant increase in conductivity as well as the plating/stripping current densities. Increased Zn(TFSI)2 salt concentration in a 2.0 M DMA in THF solvent mixture not only leads to a higher current density and conductivity, but also a higher molar conductivity due to a redissociation mechanism. The findings in this study are relevant and important to further understand and characterize multivalent electrolytes from a simple and effective electrolyte design strategy.

Redistributing Li-ion flux and homogenizing Li-metal growth by N-doped hierarchically porous membranes for dendrite-free Lithium metal batteries

Safety hazards caused by lithium dendrites significantly impedes the practical applications of Li metal batteries. However, the previously reported materials with low porosity can be easily filled up by the deposition of Li and loss of regulating effect for lithium dendrites as a Li metal protecting interlayer. Herein, scalable N-doped hierarchically porous membranes (NHPM) with significant porosity of about 90% are reported. The interconnecting porous networks with carbon nanotubes (CNTs) as the cores and N-doped carbon coating as the crosslinked shells allow the uniform distribution of Li+ ions. It also facilitates the rapid diffusion of Li ions and promotes the reversible Li plating and stripping processes. The first-principle calculations reveal that the N active sites that promote Li adsorption can greatly reduce the energy barrier for Li-ion transfer and diffusion on the carbon-coated surface. The protected Li anode exhibits a high Coulombic efficiency of ~99% and presents dendrite free morphology even when repeated Li plating/stripping processes are conducted over 500 h under condition of high current density (8 mA cm−2). A full cell battery with LiFePO4 as the cathode and protected Li as the anode exhibits high cycling stability (up to 600 cycles). The capacity decay rate is as low as 0.03% per cycle.

Delineating the Lithium–Electrolyte Interfacial Chemistry and the Dynamics of Lithium Deposition in Lithium–Sulfur Batteries

AbstractStabilizing the metallic lithium anode is the major roadblock to realizing long cycle life lithium‐sulfur (Li–S) batteries with high energy density. The chemistry of the dynamically evolving solid‐electrolyte interphase layer on the lithium surface is critical to achieving reversible plating and stripping of lithium. Herein, electrolyte formulations are carefully varied and employed to modulate the composition, and thereby, the properties of the lithium‐electrolyte interface. The impact of these changes in the interfacial chemistry on the dynamics of lithium deposition is evaluated by tracking cyclability in an anode‐free full cell configuration. Critical insights are revealed on the role of different components of the electrolyte and their interplay, including various functional groups in the electrolyte salt, oxidizing effect of lithium nitrate, and the intrinsically stabilizing effect of polysulfide species, in determining the characteristics of lithium deposition and lithium cycling efficiency. The study illuminates the key elements underlying the unique chemistry of the lithium–electrolyte interface in Li–S batteries and it can spur further development of novel strategies toward stabilizing the lithium‐metal anode in the Li–S system.

The Role of Sodium Electrolyte Impurities in Governing Interphase Formation and Impacting Calcium Anode Electrochemical Performance

Calcium-based rechargeable batteries have received considerable interest due to high theoretical energy densities, low reduction potential of the Ca2+ cation, and high crustal abundance of calcium. The reversible plating and stripping of calcium metal has recently been demonstrated using several anion/solvent combinations, including (BF4)-/ethylene carbonate:propylene carbonate [1,2], (BH4)-/THF [3], (Bhfip)-/THF-glymes [4-6], and (BF4)-/1-ethyl-3-methylimidazolium trifluoromethanesulfonate [7]. These studies are significant advancements towards implementation of Ca-ion batteries, but the coulombic efficiencies (CE) have not yet reached high enough values for practical use. Secondary phases, including CaH2 and CaF2, likely contribute to CE suppression, but other factors, such as impurities and microstructure, have not yet been studied in detail.In this contribution, we describe the critical role that sodium plays in governing the electrochemical performance and morphology of electrodeposited calcium. Trace metal analysis reveals that sodium impurity levels vary across different sources of calcium salts; such variations are correlated with highly variable CE’s and deposition morphologies. By adding controlled levels of sodium (at the hundreds of ppm level) to calcium-based electrolytes, the CE of calcium cycling exceeds 98%, indicating significantly suppressed parasitic reactions. Additionally, sodium addition causes the dominant morphology to transition from loosely packed, ~50 nm calcium platelets to densely packed columnar structures. Detailed studies of electrolyte speciation (dielectric relaxation spectroscopy, Raman spectroscopy), electrochemical response (cyclic voltammetry, chronopotentiometry), deposit microstructure, and interphase composition (SEM, TEM, TOF-SIMS, XRD) are conducted to determine the specific role that sodium plays in directing interphase formation and microstructure evolution. Our results highlight the sensitivity of calcium electrodeposition to small changes in the electrolyte and underscore the broader need for consideration of impurity impact on redox processes in multivalent electrolyte systems.This work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

An Artificial Hybrid Solid Electrolyte Interface for Reviving Lithium Metal Battery

Lithium (Li)-metal anode has attracted extensive attention owing to its high theoretical specific capacity (3860 mAh/g), which is more than ten times to that of graphite anode (372 mAh/g). However, the notorious reactivity of Li-metal prevents their practical applications due to undesired Li dendrite growth and unstable solid electrolyte interphase (SEI) formation. Here, we developed a facile, cost-effective and one-step approach for creating an artificial Li-metal/electrolyte interface by treating Li metal anode with an electrolyte containing SnF2. As a result, the artificial SEI composed of LiF, Sn and Sn-Li alloy was formed with higher ionic conductivity and increased Young’s modulus. The higher ionic conductivity and larger Young’s modulus of the artificial layer facilitate fast Li-ion diffusion and suppress Li dendrite growth, respectively. The hybrid artificial SEI showed a synergistic effect of storing Li by a reversible Sn-Li alloy formation and Li plating underneath the SEI. The artificial SEI treated Li symmetrical cells showed outstanding plating/stripping cycles (~2325 hrs) with reduced overpotential compared to the bare Li. Coupled with a high-loading (11.88 mg.cm-2) LiNi1/3Co1/3Mn1/3O2 (NMC111) cathode, the SEI protected Li full cells exhibited remarkable performance such as longer stable cycling, higher capacity retention and higher capacity at higher rates compared to the bare Li anode.

(Invited) Fluorinated Hybrid Solid-Electrolyte-Interphase for Dendrite-Free Lithium Deposition

Lithium (Li)-metal anode has attracted extensive attention owing to its high theoretical specific capacity (3860 mAh/g), which is more than ten times to that of graphite anode (372 mAh/g). However, the notorious reactivity of Li-metal prevents their practical applications due to undesired Li dendrite growth and unstable solid electrolyte interphase (SEI) formation. Here, we developed a facile, cost-effective and one-step approach for creating an artificial Li-metal/electrolyte interface by treating Li metal anode with an electrolyte containing SnF2. As a result, the artificial SEI composed of LiF, Sn and Sn-Li alloy was formed with higher ionic conductivity and increased Young’s modulus. The higher ionic conductivity and larger Young’s modulus of the artificial layer facilitate fast Li-ion diffusion and suppress Li dendrite growth, respectively. The hybrid artificial SEI showed a synergistic effect of storing Li by a reversible Sn-Li alloy formation and Li plating underneath the SEI. The artificial SEI treated Li symmetrical cells showed outstanding plating/stripping cycles (~2325 hrs) with reduced overpotential compared to the bare Li. Coupled with a high-loading (11.88 mg.cm-2) LiNi1/3Co1/3Mn1/3O2 (NMC111) cathode, the SEI protected Li full cells exhibited remarkable performance such as longer stable cycling, higher capacity retention and higher capacity at higher rates compared to the bare Li anode.

(Invited) Intercalation-Type Cathode Materials for Nonaqueous Calcium-Ion Batteries

Calcium-ion batteries (CIBs) represent a promising alternative to the current lithium-ion batteries (LIBs). Calcium ions can transfer two electrons per ion. Thus, in principle, the capacity of a host material can double due to the divalency of calcium, provided the host material can release and accept the transferred electrons. The final battery product is expected to be cost-effective, owing to the earth-abundance of calcium reserves. The redox potential of calcium is close to that of lithium, enabling a high cell voltage. The larger ionic radius of calcium (1.0 Å) compared to those of other divalent ions (0.60–0.74 Å) could be a disadvantage because a narrow diffusion pathway sufficient for smaller ions will not allow the passage of larger Ca ions. However, the larger ionic radius ensures a lower effective intercalant-ion charge density, which can be rather advantageous for the diffusion in the host materials as well as in the electrolytes.Recent discoveries of reversible plating or alloying of calcium provoked considerable interest in calcium-based rechargeable batteries. Theoretical calculations also predict that the energy barriers for Ca diffusion are lower than other multivalent ions in some structures, and the development of positive materials are anticipated. However, only a few cathode materials have been reported so far, only to exhibit low energy-storage capability and poor cyclability. In this talk, the synthesis, structural and electrochemical properties of new cathode materials for nonaqueous CIBs will be presented, which were recently developed in our group. Some examples include NASICON-type NaV2(PO4)3, FeV3O9∙1.2H2O, Ca0.13MoO3·(H2O)0.41. These stimulating discoveries will lead to the development of new strategies for obtaining high energy density CIBs.

Revealing and Elucidating ALD‐Derived Control of Lithium Plating Microstructure

AbstractThe practical implementation of Li metal batteries is hindered by difficulties in controlling the Li metal plating microstructure. While previous atomic layer deposition (ALD) studies have focused on directly coating Li metal with thin films for the passivation of the electrode–electrolyte interface, a different approach is adopted, situating the ALD film beneath Li metal and directly on the copper current collector. A mechanistic explanation for this simple strategy of controlling the Li metal plating microstructure using TiO2 grown on copper foil by ALD is presented. In contrast to previous studies where ALD‐grown layers act as artificial interphases, this TiO2 layer resides at the copper–Li metal interface, acting as a nucleation layer to improve the Li metal plating morphology. Upon lithiation of TiO2, a LixTiO2 complex forms; this alloy provides a lithiophilic surface layer that enables uniform and reversible Li plating. The reversibility of lithium deposition is evident from the champion cell (5 nm TiO2), which displays an average Coulombic efficiency (CE) of 96% after 150 cycles at a moderate current density of 1 mA cm−2. This simple approach provides the first account of the mechanism of ALD‐derived Li nucleation control and suggests new possibilities for future ALD‐synthesized nucleation layers.

Reversible Calcium-Ion Insertion in NASICON-Type NaV2(PO4)3

The recent discovery of reversible plating and alloying of calcium has invoked considerable interest in calcium-based rechargeable batteries toward overcoming the limitations of conventional Li-ion batteries. However, only a few cathode materials have been tested thus far, and these exhibit low energy-storage capability and poor cyclability. Herein, the highly reversible Ca-intercalation capability of NASICON-type NaV2(PO4)3 makes it a potential cathode material for nonaqueous Ca-ion batteries, with high capacity and voltage and good cyclability (90 mA h g–1 and ∼3.4 V at 11.7 mA g–1 and 75 °C; 70 mA h g–1 and ∼3.2 V at 5.85 mA g–1 and 25 °C). Although this work shows only the capability of the cathode, not a full-cell performance, it does demonstrate experimentally that a poly-oxyanionic material can provide an outstanding host structure for Ca diffusion at room temperature with high energy-storage capability.

Redistributing Li-Ion Flux by Parallelly Aligned Holey Nanosheets for Dendrite-Free Li Metal Anodes.

Li metal is the most ideal anode material to assemble rechargeable batteries with high energy density. However, nonuniform Li-ion flux during repeated Li plating and stripping leads to continuous Li dendrite growth and dead Li formation, which causes safety risks and short lifetime and thus impedes the commercialization of Li metal batteries. Here, parallelly aligned holey nanosheets on a Li metal anode are reported to simultaneously redistribute the Li-ion flux in the electrolyte and in the solid-electrolyte interphase, which allows uniform Li-ion distribution as well as fast Li-ion diffusion for reversible Li plating and stripping. With holey MgO nanosheets as an example, the protected Li anodes achieve Coulombic efficiency of ≈99% and ultralong-term reversible Li plating/stripping over 2500 h at a high current density of 10 mA cm-2 . A full-cell battery, using the protected anode, a 4 V Li-ion cathode, and a commercial carbonate electrolyte, shows capacity retention of 90.9% after 500 cycles.

Investigation of the Effects of Charging Processes on Lithium-Ion Cells with SiC Anodes at Low Temperatures

Lithium-ion cells with a silicon-graphite (SiC) anode and a nickel-rich cathode are potential candidates for use in electric vehicles (EVs) as this material combination offers high energy densities and low costs. Another desired cell specification that results from an intended short charging time for EVs is the robustness against high charge rates. However, high charge rates can lead to the critical aging mechanism of lithium plating, especially at low temperatures. Investigating this issue, this paper presents a test series on cyclic aging with varying charge rates from 0.2C to 1.5C at ambient temperatures of 0 °C and 10 °C applied to a nickel-rich SiC cell candidate. The resulting effects on cell aging are analyzed with a stripping method, whereby reversible lithium plating can be detected, and a differential voltage analysis (DVA), whereby the overall loss of capacity can be attributed to changes in individual characteristic capacities. The results indicate a degradation sensitivity of SiC anodes at elevated charge rates, evidenced by the loss in the silicon-related characteristic capacity, and question the aging robustness of this material combination.

Determination of Possible Reversible Lithium Plating through Electrochemical Analysis at 30 °C in Lithium Ion Cells

Fast charging of lithium ion cells is an important hurdle to overcome for the increased penetration of electric vehicles into the transportation market. During the fast charging of lithium ion cells with today’s current negative electrode active materials, namely graphite, lithium metal plating has a high likelihood of occurring. This occurs as most of the lithiated graphite potential is within 100 mV of Li/Li+ potential where a small polarization can result in lithium metal plating on the negative electrode. This plating leads to safety issues, and capacity fade, among other things. As the lithium metal is plated on the graphite negative electrode it can either become isolated and inactive, resulting in a loss of active lithium and capacity fade in the cell, or the lithium remains active during cell cycling where it may either migrate into the negative electrode over time or travel to the cells positive electrode during discharge.To date most lithium metal plating identification techniques, involve destructive physical analysis. The current study presents an electrochemical approach and technique which may identify reversible lithium metal plating on graphite negative electrodes during fast charging of lithium ion cells.

Stabilizing Anode-Free Lithium Batteries Via External Thermal Gradients

Temperature is known to have a profound impact on battery electrochemistry and performance due to the strong temperature-dependence of kinetics and diffusion. However, the role of temperature on battery behavior has mostly been considered in the case of an isothermal cell. Though active thermal management systems for batteries strive to maintain isothermal control, localized thermal gradients can still develop within individual cells, which can significantly influence local electrochemistry. For this reason, it is important to understand the consequences and also the potential benefits of non-uniform temperature distribution across batteries.Thermal gradients have been applied to lithium symmetric cells to significantly improve performance and stability. The direction of an interelectrode thermal gradient governs lithium plating morphology and dictates whether unstable, one-dimensional Li electroplating or stable, homogeneous electroplating occurs (1). With a warm positive electrode (40°C) and a cold negative electrode (0°C) (negative thermal gradient) we observe unstable cell behavior, extensive side reactions between Li and the electrolyte, and internal shorting. Reversing these temperatures so that the negative electrode is warmer than the positive electrode (a “positive” thermal gradient) decreases overpotentials, minimizes deleterious side reactions between Li and the electrolyte, and encourages long cycle life. Additionally, a positive thermal gradient stabilizes high-rate plating and stripping (1), showing promise for enabling fast-charging in lithium metal batteries.This presentation will discuss the impact of thermal gradients on stabilizing lithium plating and stripping and its application for improving long-term cycle life in anode-free lithium metal batteries. First, we will use symmetric Li metal coin cells to investigate the roles of thermal gradient magnitude and electrode temperatures on lithium plating stability. After identifying optimal thermal conditions for highly reversible Li plating and stripping, we will apply this thermal gradient to an anode-free full cell with LiFePO4 cathode to confirm its benefit on long-term cycling in a practical cell. Operando techniques, such as optical microscopy and internal thermal sensing, as well as post mortem materials characterization, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy, will be used to describe and characterize cell behavior in the presence of an applied thermal gradient.

(Invited) Nasicon-Type NaV2(PO4)3 As a Cathode Material for Calcium-Ion Batteries

Li-ion batteries (LIBs) have been the most prevailing rechargeable batteries for the last three decades. However, the present LIBs have energy densities close to the theoretical limits, and the Li resources are scarce. Calcium-ion batteries (CIBs) are one of the promising candidates to overcome such limitations of LIBs. The divalency of calcium as the carrier ion can increase the capacity of a host material because two electrons are transferred per carrier ion. The earth-abundance of calcium resources provides potential cost-effectiveness to the products. Calcium has the redox potential (Ca/Ca2+ = −2.87 V vs. SHE) close to Li, potentially leading to a higher cell operating voltage. Calcium ion also has a relatively low effective intercalant-ion charge density (0.49 e/Å3), compared to other multivalent cations such as Mg2+ (1.28 e/Å3), Zn2+ (1.18 e/Å3), and Al3+ (4.55 e/Å3), enabling fast diffusion kinetics for Ca ions in solids as well as in electrolytes. Recent discoveries of reversible plating or alloying of calcium provoked considerable interest in calcium-based rechargeable batteries. Theoretical calculations also predict that the energy barriers for Ca diffusion are lower than other multivalent ions in some structures, and the development of positive materials are anticipated. However, only a few positive materials have been reported so far, only to exhibit low energy-storage capability and poor cyclability. In this work, we report NASICON-type NaV2(PO4)3 as a cathode material for nonaqueous CIBs, with high capacity and voltage with a good cyclability. This work demonstrates experimentally that an oxide material can be a good host structure for Ca diffusion at room temperature with high energy-storage capability.

A Biphasic Interphase Design Enabling High Performance in Room Temperature Sodium-Sulfur Batteries

Summary Room temperature sodium-sulfur batteries possess higher specific energy and improved inherent safety compared to their high-temperature analogs used in stationary grid storage. The viability of room temperature sodium batteries depends critically on the mechanical and ionic transport properties of the solid electrolyte interphase. However, little emphasis has been placed on developing sodium anode interphases that combine high Young’s modulus (stiffness), high critical strain (ductility), and low ionic diffusion barrier for cycling at high rates. Here, we report an artificial biphasic interphase comprising two chemically distinct phases, NaOH and NaNH2, which combines high stiffness and high ductility. In addition, the biphasic interphase exhibits a low diffusion barrier for sodium ions, enabling reversible sodium plating and stripping behavior even at extremely high current densities (up to 50 mA cm−2) in symmetric cell configuration. Stable and reversible cycling of a room temperature sodium-sulfur battery is also demonstrated over 500 cycles.

High reversible Li plating and stripping by in-situ construction a multifunctional lithium-pinned array

Lithium metal is the most promising anode candidate because of its ultrahigh theoretical specific capacity. Unfortunately, its high reactivity, uncontrolled dendrites, “dead lithium” formation, and infinite volume expansion hinder its commercial application. Herein, by in-situ constructing a multifunctional lithium-pinned array (m-LPA) endowed with functions of lithiophilicity, zoning effect and riveting effect on a surfacely phosphorized three-dimensional (3D) copper foam, a high reversible Li plating/stripping electrochemistry can be achieved. Benefiting from the m-LPA, lithium can uniformly plate/strip both on the surface and in the inner space of the 3D skeletons with improved morphology. Consequently, a high Coulombic efficiency (~98.41%) could be achieved at 1 ​mA ​cm−2 with 1 ​mA ​h cm−2 for over 600 cycles (1200 ​h). Moreover, at a higher current density of 10 ​mA ​cm−2 with 0.5 ​mA ​h cm−2, a symmetric cell with m-LPA@Li electrode could still stably cycle for 900 cycles. Finally, a full cell coupled with LiFePO4 cathode displayed excellent rate performance with a lower overpotential. The conception and strategy of m-LPA, which were first proposed here, are a promising way to realize large-scale application of Li anode.

Preparation of Magnesium Salts Composed of Perfluoro Anions and These Electrochemical Behaviors in Molten Salts

Magnesium secondary batteries are expected to be one of the popular post-lithium ion batteries due to their high capacity and the bountiful resources of this element. Reversible plating by the reduction of Mg2+ and stripping by the oxidation of Mg metal are critical problems for this battery. In this study, we attempted to investigate the dependence of the Mg plating/stripping behavior on the anion species. Various Mg salts containing perfluoro anions were synthesized and their thermal stabilities were measured by thermogravimetry. For the Mg salts possessing a high thermal stability, Mg molten salt electrolytes were developed with potassium or cesium salts having common anions and their plating/stripping behaviors were investigated.

High energy density anodes using hybrid Li intercalation and plating mechanisms on natural graphite

A novel Li-Ion battery anode is presented which leverages the good performance of industrial graphite anodes and enhances their performance by allowing for reversible Li plating on their surface.

Rechargeable Intermetallic Calcium-Lithium-O2 Batteries.

The growing demand for rechargeable batteries with high energy density has triggered research on batteries based on polyvalent cations such as Ca2+ , Mg2+ , Al3+ , and Y3+ . Ca is, in particular, a promising anode material as an alternative to Li because of its mechanical strength (ρ=1.55 g cm-3 ), safety in terms of thermal runaway (m.p.=839 °C), earth-abundance (world production of 150 million tons of gypsum in 2012), high specific charge capacity (1.340 mAh g-1 or 2.077 mAh cm-3 ), and standard reduction potential (-2.87 V vs. normal hydrogen electrode, NHE) comparable to that of Li. As with Mg, the practical application of Ca in rechargeable batteries with organic liquid electrolytes has been hindered by the passivation layer resulting from undesirable reactions between metallic Ca and electrolytes, which precludes the possibility of reversible plating of any metal cations on Ca electrodes. Here, a battery system based on intermetallic CaLi2 anodes was developed. Li was used as a host for Ca through the formation of an intermetallic compound, which simultaneously enabled 1) the assembly of a rechargeable battery system with Ca anodes and liquid organic electrolytes and 2) coupling these with an earth-abundant, high-energy-density air cathode without special passivation agents. This strategy is simple and broadly applicable to the other polyvalent cations listed above, opening a new avenue to further engineer the electrode materials required for practical, efficient electrochemical energy-storage systems.