Sodium Metal Anode Research Articles

Long-life and high-power Sodium-Selenium Batteries realized by Vanadium single atom catalyzed cathodes and tailored carbonate-based electrolytes

The practical implementation of resources-abundant sodium-selenium batteries (SSBs) has been retarded by the low-capacity utilization and poor reversibility from the sluggish conversion kinetics of selenides, the notorious polyselenides shuttling effect and the dendritic deposition of sodium metal. This work presents a rational design of vanadium single atom catalyst on nitrogen-doped carbon sheets (V-N-C) as selenium host to address the instability of cathodes. Density function theory calculations reveal the superiority of V-N4 in V-N-C over other transition metal and nitrogen atoms in facilitating the adsorption-diffusion-conversion of polyselenides. Se@V-N-C cathodes deliver a high capacity utilization (603 mAh g−1 at 0.1 C, over 89 % of theoretical capacity), excellent reversibility (470 mAh g-1 at 0.1 C after 500 cycles), and remarkably high-power cyclability (260 mAh g−1 at 5 C over 1000 cycles). The prolong cycle life can also be originated from our tailored NaPF6 carbonate electrolyte with 1 wt% LiDFBOP additive. The new electrolyte is illustrated to generate inorganic-rich solid electrolyte interphase layers to protect sodium metal anodes from polyselenides corrosion and dendritic deposition at high rates. Fundamental findings in this work present a two-pronged approach to the prevailing challenges in the nascent metal-selenium battery chemistry.

Unveiling a Promising Active Host Material for Sodium Metal Anodes through V2AlC MAX Derivation

Unveiling a Promising Active Host Material for Sodium Metal Anodes through V₂AlC MAX Derivation

Dendrite suppression enabled longevous sodium metal batteries by sodiophilic Zein/MXene nanofiber modulated polypropylene separator

Sodium metal batteries with low-cost and high-energy density are considered as the most promising candidate for large-scale energy storage systems. However, dendritic growth of sodium metal anode (SMA) severely hampered their viability. Here, we propose the use of polypropylene separators coated by electrospinning nanofibers containing corn protein (Zein) molecules and MXene (V2CTx) sheets on polyacrylonitrile (PAN) skeletons (denoted as PZM) to tackle these issues. The abundant sodiophilic functional groups on Zein and V2CTx as well as the porous network of electrospinning nanofibers can facilitate homogeneous Na metal deposition and achieve dendrite-free SMA. Additionally, the oxygen- and nitrogen-containing functional moieties on the nanofibers benefit the electrolyte up take (395 %), ion-conductivity (1.43 mS cm−1), Na+transference number (0.77) and inorganic-rich SEI. The PZM separator enables Na metal electrodes in symmetric cells to cycle over 3500 h with a stable overpotential of 10 mV at 1 mA cm−2/1 mAh cm−2 and over 1200 h at 5 mA cm−2/10 mAh cm−2. When tested in Na3V2(PO4)3@C||Na full cells, the PZM separator enables a high capacity of 86.2 mAh g−1 over 1000 cycles with an excellent capacity retention of 87.8 %. The proposed biomaterial-based separator modification strategy can spur the development of feasible sodium metal batteries.

NaBix/NaVyOz Hybrid Interfacial Layer Enables Stable and Dendrite-Free Sodium Anodes.

The challenges of sodium metal anodes, including formation of an unstable solid-electrolyte interphase (SEI) and uncontrolled growth of sodium dendrites during charge-discharge cycles, impact the stability and safety of sodium metal batteries. Motivated by the promising commercialization potential of sodium metal batteries, it becomes imperative to systematically explore innovative protective interlayers specifically tailored for sodium metal anodes. In this work, a NaBix/NaVyOz hybrid and porous interfacial layer on sodium anode is successfully fabricated via pretreating sodium with bismuth vanadate. The hybrid interlayer effectively combines the advantages of sodium vanadates and alloys, raising a synergistic effect in facilitating sodium deposition kinetics and inhibiting the growth of sodium dendrites. As a result, the modified sodium electrodes (BVO-Na) can stably cycle for 2000h at 0.5mAcm-2 with a fixed capacity of 1mAhcm-2, and the BVO-Na||Na3V2(PO4)3 full cell sustains a high capacity of 94 mAh g-1 after 600 cycles at 5C. This work demonstrates that constructing an artificial hybrid interlayer is a practical solution to obtain high performance anodes in sodium metal batteries.

Fluorine Rich Borate Salt Anion Based Electrolyte for High Voltage Sodium Metal Battery Development.

This study demonstrates the enhanced performance in high-voltage sodium full cells using a novel electrolyte composition featuring a highly fluorinated borate ester anion (1M Na[B(hfip)4].3DME) in a binary carbonate mixture (EC:EMC), compared to a conventional electrolyte (1M Na[PF6] EC:EMC). The prolonged cycling performance of sodium metal battery employing high voltage cathodes (NVPF@C@CNT and NFMO) is attributed to uniform and dense sodium deposition along with the formation of fluorine and boron-rich solid electrolyte interphase (SEI) on the sodium metal anode. Simultaneously, a robust cathode electrolyte interphase (CEI) is formed on the cathode side due to the improved electrochemical stability window and superior aluminum passivation of the novel electrolyte. The CEIs on high-voltage cathodes are discovered to be abundant in C-F, B-O, and B-F components, which contributes to long-term cycling stability by effectively suppressing undesirable side reactions and mitigating electrolyte decomposition. The participation of DME in the primary solvation shell coupled with the comparatively weaker interaction between Na+ and [B(hfip)4]- in the secondary solvation shell, provides additional confirmation of labile desolvation. This, in turn, supports the active participation of the anion in the formation of fluorine and boron-rich interphases on both the anode and cathode.

High-Strength, Thin, and Lightweight Solid Polymer Electrolyte for Superior All-Solid-State Sodium Metal Batteries.

The utilization of solid polymer electrolytes (SPEs) in all-solid-state sodium metal batteries has been extensively explored due to their excellent flexibility, processability adaptability to match roll-to-roll manufacturing processes, and good interfacial contact with a high-capacity Na anode; however, SPEs are still impeded by their inadequate mechanical strength, excessive thickness, and poor stability with Na anodes. Herein, a robust, thin, and cost-effective polyethylene (PE) film is employed as a skeleton for infiltrating poly(ethylene oxide)-sodium bis(trifluoromethanesulfonyl)imide (PEO/NaTFSI) to fabricate PE-PEO/NaTFSI SPE. The resulting SPE features a remarkable thickness of 25 μm, lightweight property (2.1 mg cm-2), superior mechanical strength (tensile strength = 100.3 MPa), and good flexibility. The SPE also shows an ionic conductivity of 9.4 × 10-5 S cm-1 at 60 °C and enhanced interfacial stability with a sodium metal anode. Benefiting from these advantages, the assembled Na-Na symmetric cells with PE-PEO/NaTFSI show a high critical current density (1 mA cm-2) and excellent long-term cycling stability (3000 h at 0.3 mA cm-2). The all-solid-state Na||PE-PEO/NaTFSI||Na3V2(PO4)3 coin cells exhibit a superior cycling performance, retaining 93% of the initial capacity for 190 cycles when matched with a 6 mg cm-2 cathode loading. Meanwhile, the pouch cell can work stably after abuse testing, proving its flexibility and safety. This work offers a promising strategy to simultaneously achieve thin, high-strength, and safe solid-state electrolytes for all-solid-state sodium metal batteries.

Stable anode/separator interface enabled by graft modification of polypropylene separator via electron beam irradiation technique toward high-performance sodium metal batteries

Sodium metal batteries (SMBs) are considered as strong alternatives to lithium-ion batteries (LIBs), due to the inherent merits of sodium metal anodes (SMAs) including low redox potential (−2.71 V vs. SHE), high theoretical capacity (1166 mAh g−1), and abundant resources. However, the uncontrollable Na dendrite growth has significantly impeded the practical deployment of SMBs. Separator modification has emerged as an effective strategy for substantially enhancing the performance of SMAs. Herein, for the first time, we present the successful grafting polyacrylic acid (PAA) onto polypropylene (PP) separators (denoted as PP-g-PAA) using highly efficient electron beam (EB) irradiation to improve the cyclability of SMAs. The polar carboxyl groups of PAA can facilitate the electrolyte wetting and provide ample mechanical strength to resist dendrite penetration. Consequently, the regulation of Na+ ion flux enables uniform Na+ deposition with dendrite-free morphology, facilitated by the favorable anode/separator interface. The PP-g-PAA separator significantly enhances the cyclability of fabricated cells. Notably, the lifespan of Na||Na symmetric cells can be extended up to 5519 h at 1 mA cm−2 and 1 mAh cm−2. The stable design of the anode/separator interface achieved through polyolefin separator modification presented in this study holds promise for the further advancement of next-generation advanced battery systems.

An autotransferable alloy overlayer toward stable sodium metal anodes

Sodium (Na) metal anodes receive significant attention due to their high theoretical specific energy and cost-effectiveness. However, the high reactivity of Na foil anodes and the irregular surfaces have posed challenges to the operability and reliability of Na metals in battery applications. In the absence of inert environmental protection conditions, constructing a uniform, dense, and sodiophilic Na metal anode surface is crucial for homogenizing Na deposition, but remains less-explored. Herein, we fabricated a Tin (Sn) nanoparticle-assembled film conforming to separator pores, which provided ample space for accommodating volumetric expansion during the Na alloying process. Subsequently, a seamless Na-Sn alloy overlayer was formed and transferred onto the Na foil during Na plating through a separator-assisted technique, thereby overcoming conventional operational limitations of metallic Na. As compared to traditional volumetrically expanded cracked ones, the present autotransferable, highly sodiophilic, ion-conductive, and seamless Na-Sn alloy overlayer serves as uniform nucleation sites, thereby reducing nucleation and diffusion barriers and facilitating the compact deposition of metallic Na. Consequently, the autotransferable alloy layer enables a high average Coulombic efficiency of 99.9 % at 3.0 mA cm−2 and 3.0 mAh cm−2 in the half cells as well as minimal polarization overpotentials in symmetric cells, both during prolonged cycling 1200 h. Furthermore, the assembled Na||Sn-1.0h-PP||Na3V2(PO4)3@C@CNTs full cell delivers high capacity retention of 97.5 % after 200 cycles at a high cathodic mass loading.

Ionic conductive membrane suitable for sodium metal batteries

Recently, sodium-ion batteries have received great attention primarily due to the scarcity of lithium resources and fluctuations in lithium prices, but sodium-ion batteries have relatively low energy densities. One solution to the low energy density is to employ sodium metal anode, and the risks associated with using metallic sodium could be mitigated by constructing sodium-metal batteries (SMBs) with polymer electrolytes. In this paper, we would like to report a novel gel polymer membrane composed of a cellulose polymer, which not only has a wide electrochemical window, but also has excellent mechanical strength and thermal stability. Moreover, the prepared membrane exhibits high ionic conductivity, thus it can be used as separator and/or electrolyte for ionic batteries. The sodium-metal battery constructed with the prepared gel cellulose electrolyte has been further evaluated by cycling at 0.1C and 60 °C. The solid electrolyte interphase (SEI) layer formed on the surface of the sodium metal anode has been carefully examined using various characterization techniques. The results verify that the ionic-liquids based gel polymer electrolyte (IGPE) is thermally and electrochemically stable, and suitable for high-voltage SMBs.

Spatially Confined in Situ Formed Sodiophilic-Conductive Network for High-Performance Sodium Metal Batteries.

The sodium (Na) metal anode encounters issues such as volume expansion and dendrite growth during cycling. Herein, a novel three-dimensional flexible composite Na metal anode was constructed through the conversion-alloying reaction between Na and ultrafine Sb2S3 nanoparticles encapsulated within the electrospun carbon nanofibers (Sb2S3@CNFs). The formed sodiophilic Na3Sb sites and the high Na+-conducting Na2S matrix, coupled with CNFs, establish a spatially confined "sodiophilic-conductive" network, which effectively reduces the Na nucleation barrier, improves the Na+ diffusion kinetics, and suppresses the volume expansion, thereby inhibiting the Na dendrite growth. Consequently, the Na/Sb2S3@CNFs electrode exhibits a high Coulombic efficiency (99.94%), exceptional lifespan (up to 2800 h) at high current densities (up to 5 mA cm-2), and high areal capacities (up to 5 mAh cm-2) in symmetric cells. The coin-type full cells assembled with a Na3V2(PO4)3/C cathode demonstrate significant enhancement in electrochemical performance. The flexible pouch cell achieves an excellent energy density of 301 Wh kg-1.

Stable sodium metal anode enabled by interfacial room‐temperature liquid metal engineering for high‐performance sodium–sulfur batteries with carbonate‐based electrolyte

AbstractSodium (Na) metal is a competitive anode for next‐generation energy storage applications in view of its low cost and high‐energy density. However, the uncontrolled side reactions, unstable solid electrolyte interphase (SEI) and dendrite growth at the electrode/electrolyte interfaces impede the practical application of Na metal as anode. Herein, a heterogeneous Na‐based alloys interfacial protective layer is constructed in situ on the surface of Na foil by self‐diffusion of liquid metal at room temperature, named “HAIP Na.” The interfacial Na‐based alloys layer with good electrolyte wettability and strong sodiophilicity, and assisted in the construction of NaF‐rich SEI. By means of direct visualization and theoretical simulation, we verify that the interfacial Na‐based alloys layer enabling uniform Na+ flux deposition and suppressing the dendrite growth. As a result, in the carbonate‐based electrolyte, the HAIP Na||HAIP Na symmetric cells exhibit a remarkably enhanced cycling life for more than 650 h with a capacity of 1 mAh cm−2 at a current density of 1 mA cm−2. When the HAIP Na anode is paired with sulfurized polyacrylonitrile (SPAN) cathode, the SPAN||HAIP Na full cells demonstrate excellent rate performance and cycling stability.

Functional Electrolyte Additives for Sodium‐Ion and Sodium‐Metal Batteries: Progress and Perspectives

AbstractSodium‐based rechargeable batteries are considered one of the strongest contenders for the next generation of power storage devices. Functional electrolytes with additives play a crucial role in influencing the electrochemical performance of sodium‐based batteries. The addition of small doses of additives can greatly enhance the electrolyte, improving energy density, cycling performance, and safety. This paper presents an overview of recent research focused on novel additives for sodium‐ion batteries (SIBs) and sodium‐metal batteries (SMBs). The additives are categorized based on their specific functions, including film‐forming, flame retardant, overcharge protection, high‐voltage, acid and water removal, inhibition of gas production, high and low temperature and protection of sodium metal anode. The working mechanisms for these additives are thoroughly explained. Finally, potential future research directions are proposed.

Unveiling the Electro‐Chemo‐Mechanical Failure Mechanism of Sodium Metal Anodes in Sodium–Oxygen Batteries by Synchrotron X‐Ray Computed Tomography

AbstractRechargeable sodium–oxygen batteries (NaOBs) are receiving extensive research interests because of their advantages such as ultrahigh energy density and cost efficiency. However, the severe failure of Na metal anodes has impeded the commercial development of NaOBs. Herein, combining in situ synchrotron X‐ray computed tomography (SXCT) and other complementary characterizations, a novel electro‐chemo‐mechanical failure mechanism of sodium metal anode in NaOBs is elucidated. It is visually showcased that the Na metal anodes involve a three‐stage decay evolution of a porous Na reactive interphase layer (NRIL): from the initially dot‐shaped voids evolved into the spindle‐shaped voids and the eventually‐developed ruptured cracks. The initiation of this three‐stage evolution begins with chemical‐resting and is exacerbated by further electrochemical cycling. From corrosion science and fracture mechanics, theoretical simulations suggest that the evolution of porous NRIL is driven by the concentrated stress at crack tips. The findings illustrate the importance of preventing electro‐chemo‐mechanical degradation of Na anodes in practically rechargeable NaOBs.

Highly Sodiophilic Heterostructures Toward Dendrite‐Free Sodium Metal Batteries

AbstractThe utilization of Al current collector for the sodium deposition is considered ideal for achieving a low‐cost, high‐energy‐density sodium metal battery. However, the poor affinity between sodium and Al leads to uneven sodium plating/stripping, which poses a significant challenge in the pursuit of a stable sodium metal anode. Herein, a heterostructure (V/VOx)‐modified Al current collector is proposed, which effectively enables a highly reversible Na plating/stripping process, and inhibits Na dendrites growth. Experimental results and theoretical calculations demonstrate that the V/VOx@Al not only exhibits strong sodiophilicity, but also ensures a uniform current density distribution. Thanks to these merits, the assembled cells demonstrate excellent performances with low nucleation overpotential (11 mV at 1 mA cm−2), and long cycle life (2750 h) with minimal voltage polarization (13 mV at 1 mA cm−2). More impressively, the assembled full cell displays remarkable stability, sustaining 1400 cycles at 10 C. This work provides valuable insights for the development of more stable sodium metal batteries.

Tuning charge transfer and ion diffusion in 3D nanotubular arrays by engineering vacancy and implanting sodiophilic seeds for dendrite-free sodium metal anodes

Sodium metal anode (SMA) stands out as a compelling choice for future high-energy Na batteries due to its high theoretical capacity and low redox potential. However, its widespread application is severely impeded by dendrite-related hazards. Designing a host for “hostless” SMA has emerged as a promising strategy to address its harmful dendrite growth. Recent studies highlight the effectiveness of low-tortuosity arrays in SMA for guiding rapid ion transport and achieving uniform Na deposition. Herein, a pioneering 3D host, Ag@H-TNTA, characterized by low-tortuosity hydrogenated TiO2-x nanotubular arrays decorated with silver nanocrystals, are unveiled for constructing fast, stable, and dendrite-free SMA. The strategic introduction of oxygen vacancies and the implantation of sodiophilic seeds enable the achievement of rapid and coordinated electronic/ion transport as well as uniform electric-field/ion flux distribution in the Ag@H-TNTA, ultimately facilitating uniform Na deposition. Consequently, Ag@H-TNTA electrode exhibits a dendrite-free plating morphology and maintains an impressive Coulombic efficiency of ≈ 98% over 600 cycles at 1 mA cm−2 with a capacity of 1 mAh cm−2. Outstanding cycling performances and high rate capabilities of Ag@H-TNTA-Na anode are also demonstrated in both symmetric and full cells, underscoring the potential of Ag@H-TNTA as a robust host for stable and dendrite-free SMA.

Cryo-Electron Microscopy Reveals Na Infiltration into Separator Pore Free-Volume as a Degradation Mechanism in Na Anode:Liquid Electrolyte Electrochemical Cells.

Batteries utilizing a sodium (Na) metal anode with a liquid electrolyte are promising for affordable large-scale energy storage. However, a deep understanding of the intrinsic degradation mechanisms is limited by challenges in accessing the buried interfaces. Here, cryogenic electron microscopyof intact electrode:separator:electrode stacks is performed and degradation and failure of symmetric Na||Na coin cells occurs through the infiltration of Na metal through thepores of the separator rather than by mechanical puncturing by dendrites is revealed. It is shown the interior structure of the cell (electrode:separator:electrode) must be preserved anddeconstructing the cell into different layers for characterization results in artifacts. In intact cell stacks, minimal liquid is found between the electrodes and separator, leading to intimate electrode:separator interfaces. After electrochemical cycling, Na infiltrates into the pore free-volume, growing through the separator to create electrical shorts and degradation. The Na infiltration occurs at interfacial regions devoid of solid-electrolyte interphase (SEI), revealing SEI plays an important role in preventing Na from growing into the separator by being a physical barrier that the plated Na cannot penetrate. These results shed new light on the fundamental failure mechanisms in Na batteries and demonstrate the importance of preserving the cell structure and buried interfaces.

Unraveling the incompatibility mechanism of ethylene carbonate-based electrolytes in sodium metal anodes

Ethylene carbonate (EC) is widely used in lithium-ion batteries due to its optimal overall performance with satisfactory conductivity, relatively stable solid electrolyte interphase (SEI), and wide electrochemical window. EC is also the most widely used electrolyte solvent in sodium ion batteries. However, compared to lithium metal, sodium metal (Na) shows higher activity and reacts violently with EC-based electrolyte (NaPF6 as solute), which leads to the failure of sodium metal batteries (SMBs). Herein, we reveal the electrochemical instability mechanism of EC on sodium metal battery, and find that the combination of EC and NaPF6 is electrically reduced in sodium metal anode during charging, resulting in the reduction of the first coulombic efficiency, and the continuous consumption of electrolyte leads to the cell failure. To address the above issues, an additive modified linear carbonate-based electrolyte is provided as a substitute for EC based electrolytes. Specifically, ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) as solvents and fluoroethylene carbonate (FEC) as SEI-forming additive have been identified as the optimal solvent for NaFP6 based electrolyte and used in Na4Fe3(PO4)2(P2O7)||Na batteries. The batteries exhibit excellent capacity retention rate of about 80% over 1000 cycles at a cut-off voltage of 4.3 V.

Controlling Sodium Dendrite Growth via Grain Boundaries in Na3Zr2Si2PO12 Electrolyte

AbstractNa3Zr2Si2PO12(NZSP)‐based NASICON solid‐state electrolytes (SSEs) show not only competitive ionic conductivity but also high chemical stability in air, holding a great promise for enabling the use of sodium metal anode in solid‐state sodium batteries. However, sodium (Na) metal dendrite growth inside SSE always leads to undesirable short‐circuiting in battery even no obvious changes in interfacial contact loss and interfacial decomposition during cycling. How to control Na metal dendrite growth and in situ observe the effect of SSE/Na interface change on dendrite growth is quite challenging. Herein, an in situ synchrotron‐based X‐ray imaging method is developed to systematically investigate the dendrite origin in NZSP‐based SSEs. It is find that the dendrite growth intrinsically depends on the grain boundaries (GBs) in NZSP and the NZSP/Na interfacial properties. It is confirmed that Na dendrite infiltration kinetic evolution in NZSP is strongly associated with Na ion/electron conductivity and Young's modulus of GBs. Moreover, the electro‐chemo‐mechanical phase‐field model evaluation demonstrates that the basic reason for Na metal dendrite intrusion into the GBs of SSE is a combination of local polarization potential and the presence of stress formed at GBs.

Tailoring Na+ Solvation Environment and Electrode-Electrolyte Interphases with Sn(OTf)2 Additive in Non-flammable Phosphate Electrolytes towards Safe and Efficient Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries are promising for low-cost and large-scale energy storage applications. However, these batteries are plagued by safety concerns due to the highly flammable nature of conventional electrolytes. Although non-flammable electrolytes eliminate the risk of fire, they often result in compromised battery performance due to poor compatibility with sodium metal anode and sulfur cathode. Herein, we develop an additive of tin trifluoromethanesulfonate (Sn(OTf)2 ) in non-flammable phosphate electrolytes to improve the cycling stability of RT Na-S batteries via modulating the Na+ solvation environment and interface chemistry. The additive reduces the Na+ desolvation energy and enhances the electrolyte stability. Moreover, it facilitates the construction of Na-Sn alloy-based anode solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). These interphases help to suppress the growth of Na dendrites and the dissolution/shuttling of sodium polysulfides (NaPSs), resulting in improved reversible capacity. Specifically, the Na-S battery with the designed electrolyte boosts the capacity from 322 to 906 mAh g-1 at 0.5 A g-1 . This study provides valuable insights for the development of safe and high-performance electrolytes in RT Na-S batteries.

Stable sodium metal batteries by in-situ construction of multifunctional Mg-based interfacial layer in commercial carbonate-based electrolyte

Sodium metal batteries (SMBs) are attractive energy storage devices due to the low electrochemical potential of metallic sodium and large abundance of sodium element in the earth crust. However, sodium metal anode faces challenges of inevitable dendrite and unstable interface, which blocks the commercial application of SMBs. Herein, a multifunctional sodiophilic Mg-based interfacial layer is constructed on the surface of sodium metal anode by a simple and scalable in-situ reduction strategy. The Mg-based interfacial layer can effectively suppress the growth of sodium dendrite and improve the interfacial stability. First-principles calculations prove that a strong interaction is constructed between the Mg and Na atoms, which indicates that the Mg-based interfacial layer can anchor the Na atom and guide Na deposition. The calculation results also show the Mg-based interfacial layer can obviously decrease the diffusion barriers during the electrochemical process. Under the regulation of the multifunctional Mg-based interfacial layer, the electrochemical performance of symmetric and full cells is obviously improved in commercial carbonate-based electrolytes. This work provides an avenue to build protective layer on metal-based anodes for developing high-security and high-energy-density rechargeable batteries.