Metal-based Batteries Research Articles

Suppressing Dendritic Lithium Formation Using Porous Media in Lithium Metal-Based Batteries.

Because of its ultrahigh specific capacity, lithium metal holds great promise for revolutionizing current rechargeable battery technologies. Nevertheless, the unavoidable formation of dendritic Li, as well as the resulting safety hazards and poor cycling stability, have significantly hindered its practical applications. A mainstream strategy to solve this problem is introducing porous media, such as solid electrolytes, modified separators, or artificial protection layers, to block Li dendrite penetration. However, the scientific foundation of this strategy has not yet been elucidated. Herein, using experiments and simulation we analyze the role of the porous media in suppressing dendritic Li growth and probe the underlying fundamental mechanisms. It is found that the tortuous pores of the porous media, which drastically reduce the local flux of Li+ moving toward the anode and effectively extend the physical path of dendrite growth, are the key to achieving the nondendritic Li growth. On the basis of the theoretical exploration, we synthesize a novel porous silicon nitride submicron-wire membrane and incorporate it in both half-cell and full-cell configurations. The operation time of the battery cells is significantly extended without a short circuit. The findings lay the foundation to use a porous medium for achieving nondendritic Li growth in Li metal-based batteries.

Ladderlike carbon nanoarrays on 3D conducting skeletons enable uniform lithium nucleation for stable lithium metal anodes.

Inhomogeneous Li nucleation leads to uncontrolled dendritic Li growth, seriously impeding the practical applications of Li metal-based batteries. Herein, we demonstrate that a well-arranged ladderlike carbon nanoarray membrane on 3D conducting skeletons can bring about homogenous Li-ion flux and reduced local current density, thus regulating uniform Li nucleation and dendrite-free Li growth. The favorable Li deposition behavior contributes to a high Coulombic efficiency (99%) and an ultralong cycling life (1000 h) with a low overpotential.

Suppression of dendritic lithium growth in lithium metal-based batteries.

Lithium metal-based batteries offer promising prospects as alternatives to today's lithium-ion batteries, due to their ultra-high energy density. Unfortunately, the application of lithium metal is full of challenges and has puzzled researchers for more than 40 years. In this feature article, we describe the history of the development of lithium metal batteries and their existing key challenges, which include non-uniform electrodeposition, volume expansion, high reactivity of the lithium metal/unstable solid electrolyte interphase (SEI), and the shuttling of active cathode materials. Then, we focus on the growth mechanisms of uneven lithium electrodeposition and extend the discussion to the approaches to inhibit lithium dendrites. Finally, we discuss future directions that are expected to drive progress in the development of lithium metal batteries.

Operando plasmon-enhanced Raman spectroscopy in silicon anodes for Li-ion battery

Silicon, an attractive candidate for high-energy lithium-ion batteries (LIBs), displays an alloying mechanism with lithium and presents several unique characteristics which make it an interesting scientific topic and also a technological challenge. In situ local probe measurements have been recently developed to understand the lithiation process and propose an effective remedy to the failure mechanisms. One of the most specific techniques, which is able to follow the phase changes in poorly crystallized electrode materials, makes use of Raman spectroscopy within the battery, i.e., in operando mode. Such an approach has been successful but is still limited by the rather signal-to-noise ratio of the spectroscopy. Herein, the operando Raman signal from the silicon anodes is enhanced by plasmonic nanoparticles following the known surface-enhanced Raman spectroscopy (SERS). Coinage metals (Ag and Au) display a surface plasmon resonance in the visible and allow the SERS effect to take place. We have found that the as-prepared materials reach high specific capacities over 1000 mAh/g with stability over more than 1000 cycles at 1C rate and can be suitable to perform as anodes in LIB. Moreover, the incorporation of coinage metals enables SERS to take place specifically on the surface of silicon. Consequently, by using a specially designed Raman cell, it is possible to follow the processes in a silicon-coinage metal-based battery trough operando SERS measurements.

A strategy of selective and dendrite-free lithium deposition for lithium batteries

Lithium (Li) dendrite alleviation via three-dimensional (3D) structured current collectors has been well studied for Li metal-based batteries. Here we demonstrate that a hollow carbon nanofiber with proper interior to exterior radius ratio can enable Li-ions to deposit on the inner surface of the channels selectively due to the drifting effect from the structural stresses. Based on this principle, a lotus-root like structure is further designed to realize a dendrite-free hybrid Li anode with a high Li loading capability. The lotus-root like carbon nanofiber (LCNF) anode, with being coated by a lithiated Nafion (LNafion) layer as artificial solid electrolyte interface (SEI), achieves a capacity of > 3600mAh gcarbon−1 for Li deposition/stripping along with a greatly improved CE. The fundamental understanding of the relation between the Li deposition and the matrix geometry will provide new insight for the rational design of the hybrid Li anode in the Li metal-based battery system.

Three-Dimensional Copper Nanowire Sponges As Novel Current Collector for Dendrite-Free Lithium Deposition

Lithium (Li) metal, with the ultra-high theoretical capacity and the low electrochemical potential, is the ultimate anode for next-generation Li metal batteries. However, the undesirable Li dendrite growth usually results in severe safety hazards and low Coulombic efficiency. In this work, a three-dimensional (3D) conductive submicron wire sponge,fabricated using a facile one-step synthetic strategy, has been proposed to homogenize the electric field distribution on the top of Li anode, so as to inhibit the growth of Li dendrite from the root. Our experimental and simulation results show that the 3D porous structure of the Cu submicron wire sponge enables the electric field to distribute homogeneously on the top of the whole anode, and accommodates the Li deposits within its 3D porous spaces. A LiFePO4 full cell, coupled with the 3D porous Cu submicron wire sponge, shows good cycle stability as well as excellent rate capability without the Li dendrite formation after cycling. Our results obtained here provide valuable guidance and deeply understanding on the design of novel nanomaterials or structures to address the cause of the Li dendrite growth and also point out a new direction for further development of the next-generation metal-based batteries.

Nanodiamonds suppress the growth of lithium dendrites

Lithium metal has been regarded as the future anode material for high-energy-density rechargeable batteries due to its favorable combination of negative electrochemical potential and high theoretical capacity. However, uncontrolled lithium deposition during lithium plating/stripping results in low Coulombic efficiency and severe safety hazards. Herein, we report that nanodiamonds work as an electrolyte additive to co-deposit with lithium ions and produce dendrite-free lithium deposits. First-principles calculations indicate that lithium prefers to adsorb onto nanodiamond surfaces with a low diffusion energy barrier, leading to uniformly deposited lithium arrays. The uniform lithium deposition morphology renders enhanced electrochemical cycling performance. The nanodiamond-modified electrolyte can lead to a stable cycling of lithium | lithium symmetrical cells up to 150 and 200 h at 2.0 and 1.0 mA cm–2, respectively. The nanodiamond co-deposition can significantly alter the lithium plating behavior, affording a promising route to suppress lithium dendrite growth in lithium metal-based batteries.

Degradation Mechanisms of Magnesium Metal Anodes in Electrolytes Based on (CF3SO2)2N- at High Current Densities.

The energy density of rechargeable batteries utilizing metals as anodes surpasses that of Li ion batteries, which employ carbon instead. Among possible metals, magnesium represents a potential alternative to the conventional choice, lithium, in terms of storage density, safety, stability, and cost. However, a major obstacle for metal-based batteries is the identification of electrolytes that show reversible deposition/dissolution of the metal anode and support reversible intercalation of ions into a cathode. Traditional Grignard-based Mg electrolytes are excellent with respect to the reversible deposition of Mg, but their limited anodic stability and compatibility with oxide cathodes hinder their applicability in Mg batteries with higher voltage. Non-Grignard electrolytes, which consist of ethereal solutions of magnesium(II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), remain fairly stable near the potential of Mg deposition. The slight reactivity of these electrolytes toward Mg metal can be remedied by the addition of surface-protecting agents, such as MgCl2. Hence, ethereal solutions of Mg(TFSI)2 salt with MgCl2 as an additive have been suggested as a representative non-Grignard Mg electrolyte. In this work, the degradation mechanisms of a Mg metal anode in the TFSI-based electrolyte were studied using a current density of 1 mA cm-2 and an areal capacity of ∼0.4 mAh cm-2, which is close to those used in practical applications. The degradation mechanisms identified include the corrosion of Mg metal, which causes the loss of electronic pathways and mechanical integrity, the nonuniform deposition of Mg, and the decomposition of TFSI- anions. This study not only represents an assessment of the behavior of Mg metal anodes at practical current density and areal capacity but also details the outcomes of interfacial passivation, which was detected by simple cyclic voltammetry experiments. This study also points out the absolute absence of any passivation at the electrode-electrolyte interface for the premise of developing electrolytes compatible with a metal anode.

Complete Prevention of Dendrite Formation in Zn Metal Anodes by Means of Pulsed Charging Protocols.

Zn metal as anode in rechargeable batteries, such as Zn/air or Zn/Ni, suffers from poor cyclability. The formation of Zn dendrites upon cycling is the key limiting step. We report a systematic study of the influence of pulsed electroplating protocols on the formation of Zn dendrites and in turn on strategies to completely prevent Zn dendrite formation. Because of the large number of variables in electroplating protocols, a scanning droplet cell technique was adapted as a high-throughput methodology in which a descriptor of the surface roughness can be in situ derived by means of electrochemical impedance spectroscopy. Upon optimizing the electroplating protocol by controlling nucleation, zincate ion depletion, and zincate ion diffusion, scanning electron microscopy and atomic force microscopy confirmed the growth of uniform and homogenous Zn deposits with a complete prevention of dendrite growth. The implementation of pulsed electroplating as the charging protocol for commercially available Ni-Zn batteries leads to substantially prolonged cyclability demonstrating the benefits of pulsed charging in Zn metal-based batteries.

Oxygen Redox Reaction in Lithium-based Electrolytes: from Salt-in-Solvent to Solvent-in-Salt

Electrolytes are key components of Li/O2 batteries. The ionic liquid-like structure and good electrochemical and thermal stability of solvent-in-salt electrolytes make them of great interest for lithium batteries. Solutions of lithium bis(trifluoromethanesulfonyl)imide in tetraethylene glycol dimethyl-ether with molar ratios ranging from 1:9 to 1:0.9 are here investigated. A voltammetric study of oxygen redox reaction in presence of different concentrations of salt, from salt-in-solvent to solvent-in-salt solutions, is reported here for the first time along with a novel luminescence method for the evaluation of O2 solubility. The results indicate that superconcentrated solutions favor the solution formation mechanism of Li2O2 during discharge which in turn is beneficial for battery cycling stability. Despite the higher viscosity of solvent-in-salt solutions than conventional electrolytes, O2 solubility is improved at the highest salt concentrations. These findings contribute to understand electrochemical processes in solvent-in-salt solutions for Li/O2 and next generation metal-based batteries.

Development of Solid Nanocomposite Polymer Electrolyte to Enable Lithium Metal Anode Safely Cycling for High Energy Battery Application

NASA’s future missions demand advanced batteries with higher energy density, smaller volume, lighter weight and safer operation. Current state-of-the-art lithium-ion batteries (LIBs) reach the specific energy capacity limits (<250 Wh/kg), which is unable to meet the NASA’s future energy goals (>400 Wh/kg), and also pose safety issues due to using the liquid flammable electrolyte. There are intense on-going developmental activities to increase energy density. Lithium (Li)-metal based battery chemistry has the potential to achieve high-energy goals (>400 Wk/kg) to meet NASA’s future mission’s energy requirements. However, the cycle ability and safety of Li metal as anode are challenging because of morphology change and/or Li dendrite growth. Solid polymer electrolyte enhances lithium metal-based battery technology by replacing the liquid electrolyte for safety and flexible of design. However, solid polymer electrolyte has problems of low ionic conductivity (<10-3 S/cm) at ambient temperature, and compatibility issues with lithium metal anode, which act as a barrier for the practical application. Solid polymer nanocomposite electrolyte has been developed to help improve ionic conductivity, provide good compatibility with the Li electrode and mitigate the electrolyte/Li metal interfacial issue. It is a promising approach to enhance Li metal-based battery technology. In this presentation, we will present the result of solid polymer nanocomposite electrolyte to enable Li metal anode safe cycling and for high-energy battery application.

Dual Functionalities of Carbon Nanotube Films for Dendrite-Free and High Energy-High Power Lithium-Sulfur Batteries.

As a promising Li-metal battery, Li-S battery has an ultrahigh theoretical energy density of 2600 Wh kg-1. However, most of the previous work has mainly focused on tackling the "polysulfide shuttle" originating from the S cathode, while the dendrite problem coming from the Li-metal anode has often been overlooked. Herein, to solve the issues arising from both the cathode and anode simultaneously, we propose a novel cell configuration for the first time by inserting CNT films on both sides of the separator in Li-S batteries, in which the cathode-side CNT film works as a shield to suppress the "polysulfide shuttle" and the anode-side CNT film acts as a powerful shield to prevent the Li dendrite growth. In the new cell configuration, the S/rGO cathode with a high S loading of about 4.0 mg cm-2 displays a high specific capacity (1336 mAh g-1 at 0.2 C), excellent rate ability (1070, 833, 656, and 444 mAh g-1 at 0.5, 1, 2, and 5 C, respectively), and sustainable cycling stability for 150 cycles with high Coulombic efficiency (>99%) at 1 C, while the Li metal anode displays an ultrasmooth surface. We believe this work will aid in developing other metal-based (e.g., Na, K, Zn, and Al) batteries.

Boron phosphide monolayer as a potential anode material for alkali metal-based batteries

In this work, we adopt a first-principles study to evaluate the potential of a boron phosphide (BP) monolayer as an anode material for alkali metal-based (e.g., Li, Na and K) batteries.

Stabilizing lithium metal using ionic liquids for long-lived batteries

Suppressing dendrite formation at lithium metal anodes during cycling is critical for the implementation of future lithium metal-based battery technology. Here we report that it can be achieved via the facile process of immersing the electrodes in ionic liquid electrolytes for a period of time before battery assembly. This creates a durable and lithium ion-permeable solid–electrolyte interphase that allows safe charge–discharge cycling of commercially applicable Li|electrolyte|LiFePO4 batteries for 1,000 cycles with Coulombic efficiencies >99.5%. The tailored solid–electrolyte interphase is prepared using a variety of electrolytes based on the N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide room temperature ionic liquid containing lithium salts. The formation is both time- and lithium salt-dependant, showing dynamic morphology changes, which when optimized prevent dendrite formation and consumption of electrolyte during cycling. This work illustrates that a simple, effective and industrially applicable lithium metal pretreatment process results in a commercially viable cycle life for a lithium metal battery.

Ultrathin Coating of Nitrogen and Sulfur Co-Doped Graphene Nanosheets on Polymer Separator for Suppressing Dendritic Lithium Growth in Lithium Metal Batteries

The advent of electric vehicles and other high energy density applications has intensified the research efforts on lithium metal-based batteries, as metallic lithium can provide a high specific capacity (~3,862 mAh g-1), enabling it as a promising negative electrode for next-generation battery systems [1,2]. However, the instability of lithium electrodes is one of the greatest challenges hindering the successful development of lithium metal batteries. Lithium metal is unstable against nearly all chemical species and reacts with organic solvents and salts in liquid electrolytes. Moreover, continuous deposition and stripping of lithium may induce uncontrollable dendritic Li growth, which in turn leads to internal short circuits, failure, and eventually explosions. In this work, we demonstrated that an ultrathin nitrogen and sulfur co-doped graphene (NSG) layer deposited on a PE separator could effectively stabilize the lithium electrode surface, suppress dendrite formation, and improve the cycling stability of lithium metal batteries. The NSG coating layer is very thin as compared to other ceramic coatings in micrometer scales, which can provide higher energy density of the cell with NSG separator. The incorporation of heteroatom dopants could induce structural deformations due to local strains induced in the carbon framework, thereby allowing for easy ionic migration while maintaining a uniform ionic flux on the Li metal surface. Moreover, the lone pair electrons in the heteroatom dopants led to the generation of negative charge, resulting in enhanced interfacial interactions between the NSG-coated separator and the lithium electrode. The NSG coating also imparted thermal stability to the PE separator, thus preventing thermal shrinkage of the separator at elevated temperature and enhancing battery safety. The cycling performance of the lithium metal cell employing a NSG coated separator was remarkably improved as compared to the cell with a pristine PE separator.

Ultrastrong Polyoxyzole Nanofiber Membranes for Dendrite-Proof and Heat-Resistant Battery Separators.

Polymeric nanomaterials emerge as key building blocks for engineering materials in a variety of applications. In particular, the high modulus polymeric nanofibers are suitable to prepare flexible yet strong membrane separators to prevent the growth and penetration of lithium dendrites for safe and reliable high energy lithium metal-based batteries. High ionic conductance, scalability, and low cost are other required attributes of the separator important for practical implementations. Available materials so far are difficult to comply with such stringent criteria. Here, we demonstrate a high-yield exfoliation of ultrastrong poly(p-phenylene benzobisoxazole) nanofibers from the Zylon microfibers. A highly scalable blade casting process is used to assemble these nanofibers into nanoporous membranes. These membranes possess ultimate strengths of 525 MPa, Young's moduli of 20 GPa, thermal stability up to 600 °C, and impressively low ionic resistance, enabling their use as dendrite-suppressing membrane separators in electrochemical cells. With such high-performance separators, reliable lithium-metal based batteries operated at 150 °C are also demonstrated. Those polyoxyzole nanofibers would enrich the existing library of strong nanomaterials and serve as a promising material for large-scale and cost-effective safe energy storage.

Composite lithium metal anode by melt infusion of lithium into a 3D conducting scaffold with lithiophilic coating

Lithium metal-based battery is considered one of the best energy storage systems due to its high theoretical capacity and lowest anode potential of all. However, dendritic growth and virtually relative infinity volume change during long-term cycling often lead to severe safety hazards and catastrophic failure. Here, a stable lithium-scaffold composite electrode is developed by lithium melt infusion into a 3D porous carbon matrix with "lithiophilic" coating. Lithium is uniformly entrapped on the matrix surface and in the 3D structure. The resulting composite electrode possesses a high conductive surface area and excellent structural stability upon galvanostatic cycling. We showed stable cycling of this composite electrode with small Li plating/stripping overpotential (<90 mV) at a high current density of 3 mA/cm(2) over 80 cycles.

The synergetic effect of lithium polysulfide and lithium nitrate to prevent lithium dendrite growth.

Lithium metal has shown great promise as an anode material for high-energy storage systems, owing to its high theoretical specific capacity and low negative electrochemical potential. Unfortunately, uncontrolled dendritic and mossy lithium growth, as well as electrolyte decomposition inherent in lithium metal-based batteries, cause safety issues and low Coulombic efficiency. Here we demonstrate that the growth of lithium dendrites can be suppressed by exploiting the reaction between lithium and lithium polysulfide, which has long been considered as a critical flaw in lithium-sulfur batteries. We show that a stable and uniform solid electrolyte interphase layer is formed due to a synergetic effect of both lithium polysulfide and lithium nitrate as additives in ether-based electrolyte, preventing dendrite growth and minimizing electrolyte decomposition. Our findings allow for re-evaluation of the reactions regarding lithium polysulfide, lithium nitrate and lithium metal, and provide insights into solving the problems associated with lithium metal anodes.

Binding energy referencing for XPS in alkali metal-based battery materials research (I): Basic model investigations

For the investigation of chemical changes in Li- and Na-ion battery electrode systems, X-ray photoelectron spectroscopy (XPS) is a well-accepted method. Charge compensation and referencing of the binding energy (BE) scale is necessary to account for the involved mostly non-conducting species. Motivated by a conflict in energy scale referencing of Li-metal samples discussed earlier by several authors, further clarifying experimental results on several Li containing reference materials are presented and extended by similar experiments for Na. When correlating the peak positions of characteristic chemical species in all the different prepared model sample states, there seems to be a systematic deviation in characteristic binding energies of several eV if lithium is present in its metallic state. Similar results were found for sodium. The observations are furthermore confirmed by the implementation of inert artificial energy reference material, such as implanted argon or deposited gold. The behavior is associated with the high reactivity of metallic lithium and a phenomenological explanation is proposed for the understanding of the observations. Consequences for data interpretation in Li-ion battery research will be discussed for various applications in part (II).

Polymer nanofiber-guided uniform lithium deposition for battery electrodes.

Lithium metal is one of the most promising candidates as an anode material for next-generation energy storage systems due to its highest specific capacity (3860 mAh/g) and lowest redox potential of all. The uncontrolled lithium dendrite growth that causes a poor cycling performance and serious safety hazards, however, presents a significant challenge for the realization of lithium metal-based batteries. Here, we demonstrate a novel electrode design by placing a three-dimensional (3D) oxidized polyacrylonitrile nanofiber network on top of the current collector. The polymer fiber with polar surface functional groups could guide the lithium ions to form uniform lithium metal deposits confined on the polymer fiber surface and in the 3D polymer layer. We showed stable cycling of lithium metal anode with an average Coulombic efficiency of 97.4% over 120 cycles in ether-based electrolyte at a current density of 3 mA/cm(2) for a total of 1 mAh/cm(2) of lithium.