Sodium Metal Anode Research Articles

Patterned interlayer enables a highly stable and reversible sodium metal anode for sodium-metal batteries

An interlayer with a unique pattern arrangement can alter sodium deposition to mitigate dendrite growth and to facilitate a smooth sodium deposition. The stability of sodium metal anode improves significantly with the patterned interlayer.

The role of an elastic interphase in suppressing gas evolution and promoting uniform electroplating in sodium metal anodes

The role of ether electrolyte solvent in facilitating efficient Na metal anode cycling performance is identified to be preventing adverse gas formation and favouring a flexible conformal SEI.

Ultrahigh areal capacity and long cycling stability of sodium metal anodes boosted using a 3D-printed sodiophilic MXene/rGO microlattice aerogel.

Sodium metal has emerged as a highly promising anode material for sodium-based batteries, owing to its intrinsic advantages, including its high theoretical capacity, low working plateau and low cost. However, the uncontrolled formation of sodium dendrites accompanied by unrestricted volume expansion severely limits its application. To tackle these issues, we propose an approach to address these issues by adopting a three-dimensional (3D) structure of Ti3C2Tx/reduced graphene oxide (Ti3C2Tx/rGO) constructed by a direct-ink writing (DIW) 3D printing technique as the Na metal anode host electrode. The combination of the 3D-printed rGO skeleton offering artificial porous structures and the incorporation of sodiophilic Ti3C2Tx nanosheets provides abundant nucleation sites and promotes uniform sodium metal deposition. This specially designed architecture significantly enhances the Na metal cycling stability by effectively inhibiting dendrite formation. The experimental results show that the designed Ti3C2Tx/rGO electrode can achieve a high coulombic efficiency (CE) of 99.91% after 1800 cycles (3600 h) at 2 mA cm-2 with 2 mA h cm-2. Notably, the adopted electrodes exhibit a long life span of more than 1400 h with a high CE over 99.93% when measured with an ultra-high capacity of 50 mA h cm-2 at 5 mA cm-2. Furthermore, a 3D-printed full cell consisting of a Na@Ti3C2Tx/rGO anode and a 3D-printed Na3V2(PO4)3C-rGO (NVP@C-rGO) cathode was successfully demonstrated. This 3D-printed cell could provide a notable capacity of 85.3 mA h g-1 at 100 mA g-1 after 500 cycles. The exceptional electrochemical performance achieved by the 3D-printed full cell paves the way for the development of practical sodium metal anodes.

In-Situ Photoelectron Spectroscopy Investigation of Sulfurization-Induced Sodiophilic Sites with Model Systems of α-sexithiophene and p-sexiphenyl

Uncontrollable sodium dendrite growth results in poor cycling performance and severe safety issues, hindering practical applications of sodium metal batteries (SMBs). To stabilize sodium metal anodes (SMAs), various strategies have been developed including employing anode hosts and electrolyte additives to establish protective layers. Nevertheless, the understanding of interaction mechanisms between protective materials and SMAs is still limited, which is crucial for the rational design of protective materials. In this work, we investigated the interaction mechanism between sodium metal and sulfur-containing functional groups with comparative model systems of α-sexithiophene (6T) and p-sexiphenyl (6P) through in-situ photoelectron spectroscopy investigations and density functional theory (DFT) calculations. Our results show that sodium atoms tend to interact with sulfur atoms and their connected carbon atoms simultaneously as well as the aromatic carbon atoms of the end groups of 6T molecules, while no chemical interaction between Na and 6P molecules is observed. The observed sulfurization-induced sodiophilic sites can shed light on the rational design of sulfur-containing protective materials and the relevant interface engineering to stabilize SMAs.

Kinetics and Pore Formation of the Sodium Metal Anode on NASICON‐Type Na3.4Zr2Si2.4P0.6O12 for Sodium Solid‐State Batteries

AbstractIn recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next‐generation batteries. In this respect, Na3.4Zr2Si2.4P0.6O12 is a promising solid electrolyte for solid‐state sodium batteries, due to its high ionic conductivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time‐resolved impedance analysis, in situ X‐ray photoelectron spectroscopy, and transmission electron microscopy. Based on pressure‐ and temperature‐dependent impedance analyses, it is concluded that the Na|Na3.4Zr2Si2.4P0.6O12 interface kinetics is dominated by current constriction rather than by charge transfer. Cross‐sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time‐resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibration is faster and mainly caused by creep at increased external load. The presented information provides useful insights into a more profound evaluation of the sodium metal anode in solid‐state batteries.

Interface Stability between Na3Zr2Si2PO12 Solid Electrolyte and Sodium Metal Anode for Quasi-Solid-State Sodium Battery

Solid electrolytes are renowned for their nonflammable, dendrite-blocking qualities, which also exhibit stability over large potential windows. NASICON-type Na1+xZr2SixP3-xO12 (NZSP) is a well-known solid electrolyte material for sodium metal batteries owing to its elevated room temperature sodium-ion (Na+) conductivity and good electrochemical stability. Nevertheless, the strong electrode–electrolyte interfacial resistance restricts its implementation in sodium metal batteries and remains a significant challenge. In this work, we present an efficacious process to enhance the sodium wettability of Na3Zr2Si2PO12 by sputtering a thin gold (Au) interlayer. Our experimental investigation indicates a substantial reduction in interfacial resistance, from 2708 Ω cm2 to 146 Ω cm2, by employing a fine Au interlayer between the Na metal and the NZSP electrolyte. The symmetrical Na||NZSP||Na with a gold interlayer cell shows a steady Na stripping/plating at a high current density of 320 µA cm−2. A quasi-solid-state battery, with NaFePO4 (NFP) as a cathode, metallic sodium as an anode, and a Au-sputtered NZSP electrolyte with polypropylene (PP) soaked in electrolyte as an intermediate layer on the cathode, exhibited a discharge capacity of 100 mAh g−1 and a ~100% Coulombic efficiency at 50 μA cm−2 after the 50th charge/discharge cycle at room temperature (RT).

A Carboranyl Electrolyte Enabling Highly Reversible Sodium Metal Anodes via a "Fluorine-Free" SEI.

Realization of practical sodium metal batteries (SMBs) is hindered due to lack of compatible electrolyte components, dendrite propagation, and poor understanding of anodic interphasial chemistries. Chemically robust liquid electrolytes that facilitate both favorable sodium metal deposition and a stable solid-electrolyte interphase (SEI) are ideal to enable sodium metal and anode-free cells. Herein we present advanced characterization of a novel fluorine-free electrolyte utilizing the [HCB11 H11 ]1- anion. Symmetrical Na cells operated with this electrolyte exhibit a remarkably low overpotential of 0.032 V at a current density of 2.0 mA cm-2 and a high coulombic efficiency of 99.5 % in half-cell configurations. Surface characterization of electrodes post-operation reveals the absence of dendritic sodium nucleation and a surprisingly stable fluorine-free SEI. Furthermore, weak ion-pairing is identified as key towards the successful development of fluorine-free sodium electrolytes.

A Carboranyl Electrolyte Enabling Highly Reversible Sodium Metal Anodes via a “Fluorine‐Free” SEI

AbstractRealization of practical sodium metal batteries (SMBs) is hindered due to lack of compatible electrolyte components, dendrite propagation, and poor understanding of anodic interphasial chemistries. Chemically robust liquid electrolytes that facilitate both favorable sodium metal deposition and a stable solid‐electrolyte interphase (SEI) are ideal to enable sodium metal and anode‐free cells. Herein we present advanced characterization of a novel fluorine‐free electrolyte utilizing the [HCB11H11]1− anion. Symmetrical Na cells operated with this electrolyte exhibit a remarkably low overpotential of 0.032 V at a current density of 2.0 mA cm−2 and a high coulombic efficiency of 99.5 % in half‐cell configurations. Surface characterization of electrodes post‐operation reveals the absence of dendritic sodium nucleation and a surprisingly stable fluorine‐free SEI. Furthermore, weak ion‐pairing is identified as key towards the successful development of fluorine‐free sodium electrolytes.

Microarchitectures of Carbon Nanotubes for Reversible Na Plating/Stripping Toward the Development of Room‐Temperature Na–S Batteries

An ordered and homogeneous deposition of sodium metal is pivotal in achieving reversible and long‐term stability of the metal battery. The sodium deposition critically depends on the local interfacial properties of the anode/electrolyte interface. Due to the hostless nature of sodium metal anode, the integrity of the interface deteriorates rapidly, leading to a rise in stripping/plating overpotential or premature cell failure. Herein, well‐ordered microarchitectures of carbon nanotubes (MACNTs) as a potential host for reversible and highly stable stripping/plating of sodium metal are reported. Besides accommodating sodium metal, the MACNT host facilitates the formation of inorganic‐rich solid–electrolyte interphase over the sodium metal anode. As a result, it can achieve stripping/plating reversibility for 1200 h at a current of 1 mA cm−2. An overpotential of about 30 mV occurs for the stripping/plating process, indicating uniform and compact deposition of sodium. Moreover, when applying to a room‐temperature Na–FeS2 battery, the MACNT host achieves stable cycling for over 200 cycles at 200 mA g−1 and delivers a capacity of about 210 mA h g−1.

Electrodeposition of Cu-Based Nanofoams and Sodiophilic Metals for Highly Stable Anode-Free Sodium Batteries

Sodium-ion batteries (SIBs) represent a cost-effective and sustainable alternative to lithium-ion battery (LIBs).1 One of the main issues of SIB technology is the higher ionic radius of sodium, compared to lithium, which limits the cyclability due to unfavourable intercalation of Na+ ions into carbon-based anodes.2 Anode-free batteries represents a promising approach to improve the cyclability, changing the working principle at the anode from intercalation of Na+ ions to electrodeposition metallic sodium.3 Moreover, thanks to the anode-free configuration the energy density of the overall device can be drastically increased. To efficiently control the electrodeposition of the metallic layer of sodium, the current collector must be carefully designed. Copper nanofoams were produced by dynamic hydrogen-bubble template (DHBT) as high-surface area template for the sodium electrodeposition, as an innovative alternative to the traditionally flat electrodes. The electrodeposition of sodiophilic materials, i.e. tin and antimony, onto the nanofoam, was also investigated to control the nucleation of the metallic layer at the anode.4 Sn and Sb baths were optimized to guarantee an homogeneous distribution of the sodiophilic metal on the nanofoam. The morphology and the composition of the nanofoams was characterized and electrochemical characterization was performed in half-cell configuration, showing coulombic efficiency higher than 99% and good cyclability for 100 cycles, for both Sn and Sb compositions compared to the bare Cu. This demonstrates the feasibility of the usage of sodiophilic nanofoams as current collectors in anode-free sodium batteries. Vaalma, C., Buchholz, D., Weil, M. & Passerini, S. A cost and resource analysis of sodium-ion batteries. Nat. Rev. Mater. 2018 34 3, 1–11 (2018).Irisarri, E., Ponrouch, A. & Palacin, M. R. Review—Hard Carbon Negative Electrode Materials for Sodium-Ion Batteries. J. Electrochem. Soc. 162, A2476–A2482 (2015).Cohn, A. P. et al. Rethinking sodium-ion anodes as nucleation layers for anode-free batteries. J. Mater. Chem. A 6, 23875–23884 (2018).Seh, Z. W., Sun, J., Sun, Y. & Cui, Y. A highly reversible room-temperature sodium metal anode. ACS Cent. Sci. 1, 449–455 (2015).

(Invited) The Behavior of High-Capacity Anodes at Low Temperature for Li-Ion Batteries

Lithium metal and alloy anodes offer the promise of improved capacity for Li-based batteries, and they could overcome low-temperature diffusion limitations associated with graphite. However, the electrochemical behavior of these materials at low temperatures has been seldom investigated, and most liquid electrolytes exhibit extremely low Coulombic efficiency (CE) for cycling of these high-capacity electrode materials at low temperatures. Here, we demonstrate an ether-based electrolyte system with carbonate additives that substantially improves the CE of lithium metal cycling down to -60 °C. Lithium metal deposited at low temperatures in this and other electrolytes shows a clear reduction in grain size with decreasing temperature, which is correlated with lower CE. Cryo-TEM and X-ray photoelectron spectroscopy investigation of the solid-electrolyte interphase (SEI) shows that this tailored electrolyte allows for greater inorganic content in the SEI at low temperatures, which enables a compact and conducting passivation layer. We further extend these studies to sodium metal anodes, which show improved CE at low temperatures compared to lithium. Finally, we investigate alloy anode materials and show that they can exhibit stable electrochemical cycling down to -40 °C, indicating the promise of these high-capacity materials for low-temperature batteries.

Sodiophilic three-dimensional carbon skeleton derived from polyacrylonitrile@zeolitic imidazolate framework fiber for dendrite-free sodium metal anode

Albeit with natural abundance, appealing theoretical capacity and low electrode potential merits, infinite volume expansion and notorious Na dendrite still hamper the implementation of sodium metal batteries (SMBs) based on Na metal anode chemistry. Herein, we prepare a 3D sodiophilic polyacrylonitrile@zeolitic imidazolate framework (PAN@ZIF) derived carbon fiber (PZC) host, targeting at enhancing Na ion deposition kinetics and reversibility. Asymmetric cell with PZC electrode yields a low nucleation potential and impressive rate capability. Symmetric cell based on Na@PZC electrode is able to achieve a superior cycling life over 4600 h at 1 mA cm−2, 1 mAh cm−2. Even at 5 mA cm−2, 5 mAh cm−2, a remarkable cycling life over 2500 h is obtained for the Na@PZC electrode. In addition, sodiophilic characteristics of the PZC host are well uncovered by the electrochemical and DFT analyses. Meanwhile, in-situ optical microscopy and SEM results clearly unravel a stable Na ion dynamic deposition process on the Na@PZC electrode surface, thereby leading to a nearly dendrite-free morphology. Assembled with a 3D printed NVP cathode (∼16.3 mg cm−2), Na@PZC anode demonstrates a high reliability in SMBs, thus making 3D PZC host a promising strategy for regulating Na metal interface stability.

Deformation-tolerant metal anodes for flexible sodium–air fiber batteries

Although flexible sodium–air (Na–air) batteries with high theoretical energy density offer promising opportunities for next-generation smart electronics, enhancing the safety and efficiency of flexible sodium metal anodes under dynamic and continuous deformation remains a challenge. Here, a flexible sodiated carbon nanotube layer to suppress dendrite growth under various deformations is demonstrated through a Fermi level-driven spontaneous synthetic process. The resulting sodiated carbon nanotube layer, which has a spontaneously formed solid–electrolyte interface and a robust interlocked structure, creates a uniformly distributed electric field and stable interface even under deformation, affording dendrite-free flexible Na metal anodes. With this deformation-tolerant Na metal anode, we have constructed a new family of highly flexible Na–air fiber batteries with excellent cycling performance for 400 cycles at a current density of 1000 ​mA·g−1 and a capacity limit of 500 mAh·g−1 under dynamic deformation. These Na–air fiber batteries can be further woven into self-powering systems to support flexible electronic devices.

Suppression of Gas Crossover and Dendrite Growth in Sodium-Gas Batteries across a Wide Operating Temperature Range.

Enabling highly stable alkali metal anodes in gas atmospheres, such as oxygen and carbon dioxide, is critical for the implementation of emerging metal-gas batteries with high energy density and improved safety. Herein, we demonstrate a three-salt electrolyte system to tackle the problems of gas crossover and uncontrolled metallic dendrite growth for all-climate sodium-gas batteries by the formation of an electrochemically/chemically stable solid electrolyte interphase that is rich in fluoride and sulfate compounds. Consequently, the sodium metal anodes present high reversible capacity (10 mAh cm-2 at 1.5 mA cm-2) and long cycle life (2000 h) in gas atmospheres across a wide operating temperature range. Using the three-salt electrolyte, all-climate sodium-oxygen and sodium-carbon dioxide batteries are demonstrated with a reversible capacity of 1000 mAh g-1 over 100 cycles at ambient temperature and good adaptability to temperatures from -60 to 60 °C.

Ion conduction in Na＋ containing ionogels based on the UiO-66 metal organic framework

▪ conducting materials are critical to the development of solid-state sodium batteries which may enable the use of sodium metal anodes. Ionogels are hybrid liquid–solid electrolytes that are made by embedding an ionic liquid into a suitable solid framework. In this study, ionogels based on the UiO-66 type metal organic framework (MOF) porous structure were prepared. Three isostructural MOFs were synthesized and used: (i) the UiO-66 material, (ii) an amine functionalized MOF (UiO-66- ▪ ) and iii) a hydroxyl functionalized MOF (UiO-66- ▪ ). A mixture of sodium bis(fluorosulfonyl)imide (NaFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI) was embedded in the pores of the MOFs. FTIR and conductivity spectroscopy were used to asses the interaction of the mobile species with the MOF structure as well as ion transport and electric relaxation properties of the materials. We found that the conductivity of the ionogels is strongly influenced by the functionalized linker used. The UiO-66- ▪ -based ionogels present an encouraging conductivity increase trend when sodium ions are present, whereas the UiO-66- ▪ -based ionogels present the highest conductivity in the order of 0.3 mScm−1 at 293 K, albeit this is very likely due to highly mobile protons. While further studies are needed to understand which species are dominating the ion conduction, this investigation offers an insight into the behavior of MOF-based ionogels and may guide further work in the field.

Sulfur Dioxide and Sulfolane as Additives in Organic Electrolytes to Develop Room-Temperature Sodium Batteries

Sodium metal anodes have attracted great attention for the development of a next generation of high-energy batteries because of their high theoretical capacity (1166 mAh·g−1), low redox potential (−2.71 V vs. SHE), and abundance. However, sodium reacts with most of the liquid electrolytes described to date and it has the shortcoming of dendrite formation during sodium deposition. Several strategies have been proposed to overcome these issues, including the incorporation of electrolyte additives. This work reports on the use of SO2 and sulfolane as additives in organic electrolytes to modify the sodium–electrolyte interphase, making the sodium plating/stripping process more robust. Not only is the process more stable in the case of sodium metal anodes, but also the use of copper substrates is enabled. In fact, high-quality sodium films on copper have been attained by adding small mole fractions of the additives, which paves the way for the development of anode-free batteries. In a general vein, this work stresses the importance of researching on compatible and cost-effective additives that can be easily implemented in practice.

Heterogeneous Interfacial Layers Derived from the In Situ Reaction of CoF2 Nanoparticles with Sodium Metal for Dendrite‐Free Na Metal Anodes

AbstractSodium‐metal batteries, with high energy density and low cost, are emerging stars in the field of large‐scale energy storage and power batteries. The application of sodium metal is hindered by side reactions between the active sodium metal anode and the electrolyte, unstable solid electrolyte interphase, and dendrite growth caused by the uneven distribution of sodium ions. Here, heterogeneous interface layer composed of the sodium fluoride and metallic cobalt (NaF/Co) is constructed in situ and spontaneously by introducing the CoF2 nanoparticles confined in carbon to the Na metal surface. The NaF/Co artificial interface layer with high Young's modulus, high Na+ conductivity, high surface energy, and strong sodiophilicity renders the Na+ evenly distributed, suppresses Na‐dendrite growth, and reduces side reaction with electrolyte. Due to these virtues, the Na||Na symmetric cells with NaF/Co interface layers demonstrate long cycle life (1000 h at 1.0 mA cm−2, 1.0 mAh cm−2). Moreover, when the NaF/Co/Na anode is matched with Na3V2(PO4)3 cathode, the produced full battery (Na3V2(PO4)3||NaF/Co/Na) exhibits a long lifespan of 1000 cycles at 15 C and a high‐rate capacity of ≈52 mAh g−1 at 60 C. This work provides a new strategy to solve the dendrite growth of Na metal anodes.

3-Trimethylsilyl-2-oxazolidinone, as a multifunctional additive to stabilize FEC-containing electrolyte for sodium metal batteries

Rechargeable sodium batteries have become an important complement to lithium secondary batteries and other energy devices due to their lithium-like operating mechanism and abundant sodium resources. Sodium metal batteries (SMBs) with high energy density can be applied in more aspects, but still faces more prominent challenges such as sodium dendrite growth and severe electrode-electrolyte interface reactions. Fluoroethylene carbonate (FEC) additive can effectively improve the stability of sodium metal anode due to the formation of a stable solid electrolyte interfacial (SEI) layer on sodium surface. However, the protective effect is not sufficient in suppressing sodium dendrite and corrosion of electrolyte as its easily ring-opening polymerization induced by Lewis acid (especially PF5) in carbonate electrolytes. Here, 3-Trimethylsilyl-2-oxazolidinone (TMSO) as a multifunctional additive that not only removes H2O and HF from the electrolyte, but also inhibits the decomposition of NaPF6 and improves the stability of FEC-containing electrolytes. Besides, TMSO can form a stable cathode electrolyte interfacial (CEI) layer on Na3V2(PO4)3 (NVP) cathode surface, alleviating NVP cracking and structural pulverization and thus endowing the long-term cycling stability of NVP cathode with low interfacial resistance. Notably, with the optimized electrolyte, the Na||NVP metal battery exhibits stable cycle performance with a capacity retention of 93.1% after 1400 cycles at room temperature and higher capacity retention of 96.6% for 270 cycles at 55 °C.

Low Na-β′′-alumina electrolyte/cathode interfacial resistance enabled by a hydroborate electrolyte opening up new cell architecture designs for all-solid-state sodium batteries

Development of low-resistance electrode/electrolyte interfaces is key for enabling all-solid-state batteries with fast-charging capabilities. Low interfacial resistance and high current density were demonstrated for Na-β′′-alumina/sodium metal interfaces, making Na-β′′-alumina a promising solid electrolyte for high-energy all-solid-state batteries. However, integration of Na-β′′-alumina with a high-energy sodium-ion intercalation cathode remains challenging. Here, we report a proof-of-concept study that targets the implementation of a Na-β′′-alumina ceramic electrolyte with a slurry-casted porous NaCrO2 cathode with infiltrated sodium hydroborates as secondary electrolyte. The hydroborate Na4(B12H12)(B10H10) possesses similar sodium-ion conductivity of 1 mS cm−1 at room temperature as Na-β′′-alumina and can be fully densified by cold pressing. Using the Na4(B12H12)(B10H10) secondary electrolyte as interlayer between Na-β′′-alumina and NaCrO2, we obtain a cathode-electrolyte interfacial resistance of only 25 Ω cm2 after cold pressing at 70 MPa. Proof-of-concept cells with a sodium metal anode and a NaCrO2 cathode feature an initial discharge capacity of 103 mAh g−1 at C/10 and 42 mAh g−1 at 1 C with an excellent capacity retention of 88% after 100 cycles at 1 C at room temperature. Ion-milled cross-sections of the cathode/electrolyte interface demonstrate that intimate contact is maintained during cycling, proving that the use of hydroborates as secondary electrolyte and as an interlayer is a promising approach for the development of all-solid-state batteries with ceramic electrolytes.

Highly Reversible Sodium Metal Battery Anodes via Alloying Heterointerfaces.

As a promising pathway toward low-cost, long-duration energy storage, rechargeable sodium batteries are of increasing interest. Batteries that incorporate metallic sodium as anode promise a high theoretical specific capacity of 1166mAhg-1 , and low reduction potential of -2.71V. The high reactivity and poor electrochemical reversibility of sodium anodes render sodium metal anode (SMA) cells among the most challenging for practical implementation. Here, the failure mechanisms of Na anodes are investigated and the authors reportthat loss of morphological control is not the fundamental cause of failure. Rather, it is the inherently poor anchoring/root structure of electrodeposited Na to the electrode substrate that leads to poor reversibility and cell failure. Poorly anchored Na deposits are prone to break away from the current collector, producing orphaning and poor anode utilization. Thin metallic coatings in a range of chemistries are proposed and evaluated as SMA substrates. Based on thermodynamic and ion transport considerations, such substrates undergo reversible alloying reactions with Na and are hypothesized to promote good root growth-regardless of the morphology. Among the various options, Au standsout for its ability to support long Na anode lifetime and high reversibility (Coulombic Efficiency > 98%), for coating thicknesses in the range of 10-1000nm. As a first step toward evaluating practical utility of the anodes, their performance in Na||SPAN cells with N:P ratio close to 1:1 is evaluated.