Na-CO2 Batteries Research Articles

Multiscale Defective Interfaces for Realizing Na-CO2 Batteries With Ultralong Lifespan.

Despite their favorable high energy density and potential for CO2 recycling, Na-CO2 batteries have been held back by limitations in cycling capability, stemming from the sluggish CO2 reduction/evolution reaction (CO2RR/CO2ER) kinetics at CO2 cathode and unmanageable deposition/stripping of metallic Na at the anode upon cycling. Herein, a "two-in-one" electrode with multiscale defective FeCu interfaces (CP@FeCu) is presented, which is capable of improving the CO2RR/CO2ER kinetics of CO2-breathing cathode, while modulating sodium deposition behavior. Experimental and theoretical investigations reveal multiscale defective FeCu interfaces are responsible for the enhancement of sodiophilicity and catalytic properties. The defect and valence oscillation effects originate in multiscale defective FeCu interfaces, effectively facilitating the adsorption of reactants and decomposition of Na2CO3 during CO2RR/CO2ER processes, along with exceptional cycling stability of 2400 cycles (4800h) at 5µAcm-2. Meanwhile, the CP@FeCu with sodium affinity creates a uniform electric field and robust adsorption for Na, making initial nucleation sites more conducive to Na deposition and achieving dendrite-resistant and durable anodes. This work offers a scientific insight into the functionalization design of "two-in-one" electrodes, which is essential for a unified solution to the challenges in sodium anodes and CO2 cathodes.

P-band regulation guides the free-standing porous carbon electrode for efficient Na-CO2 batteries

The Na-CO2 batteries with low-cost resources and high energy density have attracted huge attention in Mars and deep ocean exploration, but the slow CO2 reduction reaction (CO2RR) and CO2 evolution reaction (CO2ER) kinetics severely limit their practical application. Developing free-standing cathodes and understanding the relationship between the catalyst's active center and activity are essential to address long-standing challenges. This manuscript explores the promising metal-free porous carbon as a catalyst. The porous carbon network vertically grows on the surface of free-standing carbon paper to maximum exposure to the active site and optimization of electron/electrolyte transfer. Moreover, the active center of the carbon catalyst is optimized by introducing nitrogen or sulfur hetero-atom to regulate the p-band center, which steers the orbital hybridization and accelerates CO2RR and CO2ER kinetics The p-band optimized free-standing porous carbon electrode shows outstanding cycling of 1000 h with a small voltage gap of 1.04 V and a large energy efficiency of 71.2 % at 10 uA cm−2. This study provides a new strategy for designing and fabricating p-band guided free-standing electrodes aiming at high-performance and wearable Na-CO2 batteries.

Low-Overpotential Rechargeable Na-CO2 Batteries Enabled by an Oxygen-Vacancy-Rich Cobalt Oxide Catalyst.

Rechargeable sodium-carbon dioxide (Na-CO2) batteries have been proposed as a promising CO2 utilization technique, which could realize CO2 reduction and generate electricity at the same time. They suffer, however, from several daunting problems, including sluggish CO2 reduction and evolution kinetics, large polarization, and poor cycling stability. In this study, a rambutan-like Co3O4 hollow sphere catalyst with abundant oxygen vacancies was synthesized and employed as an air cathode for Na-CO2 batteries. Density functional theory calculations reveal that the abundant oxygen vacancies on Co3O4 possess superior CO2 binding capability, accelerating CO2 electroreduction, and thereby improving the discharge capacity. In addition, the oxygen vacancies also contribute to decrease the CO2 decomposition free energy barrier, which is beneficial for reducing the overpotential further and improving round-trip efficiency. Benefiting from the excellent catalytic ability of rambutan-like Co3O4 hollow spheres with abundant oxygen vacancies, the fabricated Na-CO2 batteries exhibit extraordinary electrochemical performance with a large discharge capacity of 8371.3 mA h g-1, a small overpotential of 1.53 V at a current density of 50 mA g-1, and good cycling stability over 85 cycles. These results provide new insights into the rational design of air cathode catalysts to accelerate practical applications of rechargeable Na-CO2 batteries and potentially Na-air batteries.

Robust Solid-State Na-CO2 Battery with Na2.7Zr2Si2PO11.7F0.3-PVDF-HFP Composite Solid Electrolyte and Na15Sn4/Na Anode.

Solid-state Na-CO2 batteries are a kind of energy storage devices that can immobilize and convert CO2. They have the advantages of both solid-state batteries and metal-air batteries. High-performance solid electrolyte and electrode materials are important for improving the performance of solid-state Na-CO2 batteries. In this work, we investigate the influence of fluorine doping on the structure and ionic conductivity of Na3Zr2Si2PO12 (NZSP). An ionic conductive solid electrolyte membrane was prepared by compositing the inorganic solid electrolyte Na2.7Zr2Si2PO11.7F0.3 (NZSPF3) with poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP). It shows an ionic conductivity of up to 2.17 × 10-4 S cm-1 at room temperature, a high sodium ionic transfer number of ∼0.70, a broad electrochemical window of ∼5.18 V, and better mechanical strength. Furthermore, we studied the Na15Sn4/Na composite foil with the ability to inhibit dendrite as the anode for solid-state Na-CO2 batteries. Through density functional theory (DFT) calculations, the Na15Sn4 particle has been verified with a strong sodiophilic property, which reduces the nucleation barrier during the deposition process, leading to a lower overpotential. The symmetric cell assembled with the composite solid-state electrolyte NZSPF3-PVDF-HFP and Na15Sn4/Na composite anode can inhibit the growth of Na dendrites effectively and maintain the stability of the whole cell structure. Solid-state Na-CO2 batteries assembled with Ru-carbon nanotube (Ru-CNTs) as cathode catalysts exhibit a high discharge capacity of 6371.8 mAh g-1 at 200 mA g-1, excellent cycling stability for 1100 h, and good rate performance. This work provides a promising strategy for designing high-performance solid-state Na-CO2 batteries.

Co3O4 nanoparticle modified N, P co-doped carbon paper as sodium carrier to construct stable anodes for Na-metal batteries.

Sodium (Na) metal batteries such as Na-ion batteries and Na-CO2 batteries are considered to be excellent alternatives to lithium batteries in terms of their potential applications because of their high specific capacity and low cost. However, the sodium anode showed low efficiency and poor cycling in Na-metal battery performance due to the formation of sodium dendrites and serious corrosion. In this work, nitrogen (N), phosphorus (P) co-doped carbon paper (NP-CP) modified with cobalt tetroxide (Co3O4) nanoparticles was prepared as the Na anode carrier (Co3O4@NP-CP), and a sodium-based composite anode (Na-Co@NP-CP) was further prepared by electrodepositing sodium. The experimental results indicate that the N, P and Co3O4 multi-doped carbon paper has good sodiophilicity, which can induce the uniform plating/stripping of Na+ ions and inhibit the growth of Na dendrites. The N, P doped carbon paper provides a high surface area and tremendous three-dimensional (3D) framework to effectively reduce the areal current density, facilitate the transfer of electrons, and enhance battery life. Therefore, Na-Co@NP-CP based symmetric cells exhibit stable cycling of over 1100 hours at current densities of 1 mA cm-2 and fixed capacity of 1 mA h cm-2. When the Na-Co@NP-CP anode couples with CO2, the assembled batteries can deliver a stable cycling of 165 cycles at current densities of 500 mA g-1 and limited capacity of 500 mA h g-1. When Na-Co@NP-CP anode couples with Na3V2(PO4)3 (NVP) cathode, the assembled cells exhibit lower hysteresis and batter cycling performance.

Unveiling the electrochemical characteristics of acetonitrile-catholyte-based Na-CO2 battery

The development of metal-CO2 batteries has attracted intense attention because of their unique electrochemical reaction for utilization of CO2 gas. However, unlike the alkali metal-based O2 batteries, a limited number of combinations of aprotic electrolytes have been employed for Li(Na)–CO2 batteries due to the sluggish reaction for the formation of the Li(Na)2CO3 discharge product. Here, we demonstrate an acetonitrile (MeCN)-based catholyte for use in a hybrid cell type Na-CO2 battery. The presence of a solid ceramic separator in our hybrid cell allows the stable operation of the MeCN catholyte-based Na-CO2 battery, resulting in improved electrochemical characteristics such as low overpotential, high energy density, and long cycle stability compared to the conventional TEGDME-based electrolyte. In particular, results of molecular dynamics simulations suggest that the improved performance is mainly due to the enhanced Na+ diffusion in the electrolyte. The calculated barrier for Na+ diffusion in MeCN is approximately four times lower than that in TEGDME. Thus, this work provides a promising electrolyte combination and reveals the mechanism for the improved performance of the MeCN-based electrolyte used in the hybrid cell structure, promoting the development of Na-CO2 batteries as practical secondary energy storage devices.

Recent Advances in Rechargeable Metal-CO2 Batteries with Nonaqueous Electrolytes.

This review article discusses the recent advances in rechargeable metal-CO2 batteries (MCBs), which include the Li, Na, K, Mg, and Al-based rechargeable CO2 batteries, mainly with nonaqueous electrolytes. MCBs capture CO2 during discharge by the CO2 reduction reaction and release it during charging by the CO2 evolution reaction. MCBs are recognized as one of the most sophisticated artificial modes for CO2 fixation by electrical energy generation. However, extensive research and substantial developments are required before MCBs appear as reliable, sustainable, and safe energy storage systems. The rechargeable MCBs suffer from the hindrances like huge charging-discharging overpotential and poor cyclability due to the incomplete decomposition and piling of the insulating and chemically stable compounds, mainly carbonates. Efficient cathode catalysts and a suitable architectural design of the cathode catalysts are essential to address this issue. Besides, electrolytes also play a vital role in safety, ionic transportation, stable solid-electrolyte interphase formation, gas dissolution, leakage, corrosion, operational voltage window, etc. The highly electrochemically active metals like Li, Na, and K anodes severely suffer from parasitic reactions and dendrite formation. Recent research works on the aforementioned secondary MCBs have been categorically reviewed here, portraying the latest findings on the key aspects governing secondary MCB performances.

Advanced Li/Na-CO2 Batteries Enabled by the γ-MnO2 Catalyst with Enhanced Carbonate Decomposition.

Metal-CO2 batteries, especially Li-CO2 and Na-CO2 batteries, are regarded as ideal new-generation energy storage systems owing to their high energy density and extraordinary CO2 capture capability. However, the advancement of metal-CO2 batteries is still at an early stage. The problems caused by accumulation of carbonates during charge-discharge cycles, such as large polarization and poor reversibility, restrict their practical application. Therefore, designing efficient catalysts is crucial for promoting the decomposition of carbonate to improve the electrochemical performance of metal-CO2 batteries. Herein, we first adopted sea urchin-like γ-MnO2 as the cathode material for Li/Na-CO2 batteries. Benefiting from the unique structure and excellent catalytic activity of γ-MnO2, the as-prepared Li-CO2 and Na-CO2 batteries can achieve low overpotentials of 1.28 and 1.36 V, respectively, at a current density of 100 mA g-1 with a cutoff capacity of 1000 mA h g-1. The overpotentials are lower than those of most of the state-of-the-art catalysts in previous reports. After 100 and 50 cycles of Li-CO2 and Na-CO2 batteries, respectively, their charging termination voltages remain at around 4.1 and 3.9 V, respectively; such a low charging platform indicates the excellent catalytic activity of the γ-MnO2 cathode on the discharge products. Our findings offer a promising guideline to design efficient electrocatalysts for high-performance metal-CO2 batteries.

Exploiting Cation Intercalating Chemistry to Catalyze Conversion-Type Reactions in Batteries

Effective harvest of electrochemical energy from insulating compounds serves as the key to unlocking the potential capacity from many materials that otherwise could not be exploited for energy storage. Herein, an effective strategy is proposed by employing LiCoO2, a widely commercialized positive electrode material in Li-ion batteries, as an efficient redox mediator to catalyze the decomposition of Na2CO3 via an intercalating mechanism. Differing from traditional redox mediation processes where reactions occur on the limited surface sites of catalysts, the electrochemically delithiated Li1-xCoO2 forms NayLi1-xCoO2 crystals, which act as a cation intercalating catalyzer that directs Na+ insertion-extraction and activates the reaction of Na2CO3 with carbon. Through altering the route of the mass transport process, such redox centers are delocalized throughout the bulk of LiCoO2, which ensures maximum active reaction sites. The decomposition of Na2CO3 thus accelerated significantly reduces the charging overpotential in Na-CO2 batteries; meanwhile, Na compensation can also be achieved for various Na-deficient cathode materials. Such a surface-induced catalyzing mechanism for conversion-type reactions, realized via cation intercalation chemistry, expands the boundary for material discovery and makes those conventionally unfeasible a rich source to explore for efficient utilization of chemical energy.

A Durable Solid‐State Na–CO2 Battery with Solid Composite Electrolyte Na3.2Zr1.9Ca0.1Si2PO12–PVDF‐HFP

Na–CO2 batteries are important devices for immobilizing CO2 and storing renewable energy. However, the Na–CO2 batteries with liquid electrolytes have the issues of electrolyte volatilization and poor cyclability. Herein, a composite solid‐state electrolyte consisting of Ca‐doped Na3Zr2Si2PO12 and polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐HFP) is synthesized. The solid composite electrolyte Na3.2Zr1.9Ca0.1Si2PO12–PVDF‐HFP shows a high ionic conductivity of 1.32 × 10−4 S cm−1 at room temperature and a broad electrochemical window up to 5.15 V, as well as excellent durability. The assembled solid‐state Na–CO2 battery with this composite electrolyte delivers a high discharge‐specific capacity up to 3320 mA h g−1 and excellent cycling stability.

Fundamental Understanding of Nonaqueous and Hybrid Na-CO2 Batteries: Challenges and Perspectives.

Alkali metal-CO2 batteries, which combine CO2 recycling with energy conversion and storage, are a promising way to address the energy crisis and global warming. Unfortunately, the limited cycle life, poor reversibility, and low energy efficiency of these batteries have hindered their commercialization. Li-CO2 battery systems have been intensively researched in these aspects over the past few years, however, the exploration of Na-CO2 batteries is still in its infancy. To improve the development of Na-CO2 batteries, one must have a full picture of the chemistry and electrochemistry controlling the operation of Na-CO2 batteries and a full understanding of the correlation between cell configurations and functionality therein. Here, recent advances in CO2 chemical and electrochemical mechanisms on nonaqueous Na-CO2 batteries and hybrid Na-CO2 batteries (including O2 -involved Na-O2 /CO2 batteries) are reviewed in-depth and comprehensively. Following this, the primary issues and challenges in various battery components are identified, and the design strategies for the interfacial structure of Na anodes, electrolyte properties, and cathode materials are explored, along with the correlations between cell configurations, functional materials, and comprehensive performances are established. Finally, the prospects and directions for rationally constructing Na-CO2 battery materials are foreseen.

Recent Progress and Perspectives of Solid State Na-CO2 Batteries

Solid state Na-CO2 batteries are a kind of promising energy storage system, which can use excess CO2 for electrochemical energy storage. They not only have high theoretical energy densities, but also feature a high safety level of solid-state batteries and low cost owing to abundant sodium metal resources. Although many efforts have been made, the practical application of Na-CO2 battery technology is still hampered by some crucial challenges, including short cycle life, high charging potential, poor rate performance and lower specific full discharge capacity. This paper systematically reviews the recent research advances in Na-CO2 batteries in terms of understanding the mechanism of CO2 reduction, carbonate formation and decomposition reaction, design strategies of cathode electrocatalysts, solid electrolytes and their interface design. In addition, the application of advanced in situ characterization techniques and theoretical calculation of metal–CO2 batteries are briefly introduced, and the combination of theory and experiment in the research of battery materials is discussed as well. Finally, the opportunities and key challenges of solid-state Na-CO2 electrochemical systems in the carbon-neutral era are presented.

“Water-in-Salt” and Nasicon Electrolyte-Based Na-CO2 Battery

Super concentrated electrolytes, referred to as “water-in-salt (WiS) electrolytes”, have been received attention due to their wide electrochemical stability window, cost-effectiveness, and non-flammability. However, the free water molecules present in WiS electrolytes prevent the use of Na-metal as the anode for Na-gas batteries.In this study, we develop a Na-CO2 battery with WiS and Na-super-ionic conductor (NASICON) electrolytes that were used as energy storage cells and CO2 gas utilization. The NASICON separator allowed us to fabricate a hybrid Na-CO2 battery comprising Na metal as the anode material and WiS as the cathode electrolyte without damage of Na metal. Additionally, linear sweep voltammetry (LSV) with corresponding differential electrochemical mass spectroscopy (DEMS) measurements rendered the direct observation of H2 evolution retardation with increasing WiS concentration. Furthermore, we introduced a nano-sized Ru catalyst onto the current collector using Joule heating method for reducing the overpotential gap. Consequently, the Na-CO2 batteries with Ru@carbon current collector reduced the overpotential gap and exhibited a cycling endurance of over 75 cycles.

Cobalt-decorated carbon nanofibers as a low overpotential cathode for nonaqueous Na-CO2 batteries

As the high energy-density energy storage and greenhouse gas capture device, Na-CO2 battery development is impeded by the sluggish CO2 reduction and difficult decomposition of insulating discharge products on the cathode. Here, the cobalt (Co)-decorated carbon nanofibers accompanying with slight Co oxidation were used as the self-standing cathode for Na-CO2 battery. It greatly reduces the discharge overpotential by 500 mV and charge overpotential by 210 mV, delivers a 12 times higher discharge capacity and runs nearly 4 times cycle life than its counterpart. Experiment combined with theory calculation demonstrates that the evenly dispersive, abundant and stable active sites (Co-CoO) with an equal CO2 adsorption-desorption capability is the key to improving cell performance. This work reveals the importance of catalysts/cathodes and provides a direction to design highly efficient catalysts/cathodes for alkali metal-CO2 batteries.

“Water-in-Salt” and Nasicon Electrolyte-Based Na-CO2 Battery

Aprotic electrolytes are much less feasible for producing cost-effective Na metal-based CO2 batteries due to high cost and flammability. As an alternative electrolyte, super-concentrated electrolytes, referred to as “water-in-salt (WiS) electrolytes”, have been received attention due to their wide electrochemical stability window, cost-effectiveness, and non-flammability. However, the highly reactive Na metal prevents the direct use of WiS electrolytes because the unsolvated water molecules would react with the Na Metal.In this study, we demonstrated the ability of a WiS and NASICON electrolyte-based Na-CO2 battery for utilizing CO2 gas and serving as an energy storage cell. The NASICON separator allowed us to fabricate a hybrid Na-CO2 battery comprising Na metal as the anode material and WiS as the cathode electrolyte without damage of Na metal. Additionally, linear sweep voltammetry (LSV) with corresponding differential electrochemical mass spectroscopy (DEMS) measurements rendered the direct observation of H2 evolution retardation with increasing WiS concentration. Furthermore, we introduced a nano-sized Ru catalyst onto the current collector using Joule heating method for reducing the overpotential gap. Consequently, the Na-CO2 batteries with Ru@carbon current collector reduced the overpotential gap and exhibit a cycling endurance of over 75 cycles. Figure 1

Fabrication of long-life quasi-solid-state Na-CO2 battery by formation of Na2C2O4 discharge product

Rechargeable Na-CO2 batteries are promising energy-storage devices due to their high energy density, environmental friendliness, and cost effectiveness. However, the insulating nature and irreversibility of the Na2CO3 discharge product cause large polarization and poor cyclicity. Here, we report a reversible quasi-solid-state Na-CO2 battery that is constructed by the synergistic action of a Co-encapsulated N-doped carbon framework catalyst and gel electrolyte to ensure the formation of a highly reversible Na2C2O4 discharge product. Experiments and density functional theory calculations indicate that the electron-agglomeration effect of Co nanoparticles enhances CO2 adsorption and lowers energy barrier, as well as promotes Na2C2O4 generation. A gel electrolyte containing an imidazole organic cation is used to inhibit the decomposition of the thermodynamically unstable Na2C2O4. The fabricated Na-CO2 battery exhibits a high discharge capacity of 3,094 mAh g−1, a high-rate performance of 1,777 mAh g−1 at a current density of 0.5 mA cm−2, and excellent cycling performance of 366 cycles (2,200 h).

Ultrafine RuO2 nanoparticles/MWCNTs cathodes for rechargeable Na-CO2 batteries with accelerated kinetics of Na2CO3 decomposition

Na-CO2 batteries have attracted extensive attention due to their high theoretical energy density (1125 Wh/kg), efficient utilization of CO2, and abundant sodium resources. However, they are trapped by the sluggish decomposition kinetic of discharge products (mainly Na2CO3) on cathode side during the charging process. Here we prepared a series of nano-composites composed of RuO2 nanoparticles in situ loaded on activated multi-walled carbon nanotubes (RuO2@a-MWCNTs) through hydrolyzing reaction followed by calcination method and used them as cathode catalysts to accelerate the decomposition of Na2CO3. Among all catalysts, the RuO2@a-MWCNTs with appropriate ratio of RuO2 (49.7 wt%) demonstrated best stability and rate performance in Na-CO2 batteries, benefiting from both high specific surface area (160.3 m2/g) and highly dispersed RuO2 with ultrafine nanostructures (∼2 nm). At a limited capacity of 500 mAh/g, Na-CO2 batteries could afford the operation of over 120 cycles at 100 mA/g, and even at the current density to 500 mA/g, the charge voltage was still lower than 4.0 V after 40 cycles. Further theoretical calculations proved that RuO2 was the catalytically active center and contributed to the decomposition of Na2CO3 by weakening the C=O bond. The synergetic functions of high specific surface (CNTs) and high catalytic activity (RuO2) will inspire more progress on metal-CO2 batteries.

Engineering NH3-induced 1D self-assembly architecture with conductive polymer for advanced hybrid Na-CO2 batteries via morphology modulation

Designing catalytic cathodes with excellent electrocatalytic activities and durability for Na-CO 2 batteries has captured considerable attention so far. Here, a series of morphologically controlled low-crystalline CuCo 2 O 4 was prepared by thermal oxidation of self-assembled Cu-Co precursors ( p -CCO). One-dimensional (1D) rod-like of CuCo 2 O 4 was subsequently encapsulated in polypyrrole shell (PPy) by in-situ polymerization of pyrrole monomers as an advanced catalyst (CCO/PPy) for high-performance Na-CO 2 batteries. It was demonstrated that ammonia solution exerts an important influence on the surface morphology and size of the p -CCO crystallites by the rate of nucleation and growth. Particle size and 1D architecture modulation, associated with the encapsulation of conductive PPy effectively improve the directional transfer rate of ions and the conductivity of the electrode. More importantly, PPy introduction not only induces interfacial reconstruction of CuCo 2 O 4 , arousing more oxygen vacancies and catalytic active sites, but also contributes to the corrosion protection of the active material from the electrolyte during long-term operation. Bestowed by these advantages, the fabricated hybrid Na-CO 2 battery manifested prominent electrochemical performance with a superior areal discharge capacity of 31.3 mAh cm −2 , low discharge-charge voltage gap of 0.6 V, over 400 cycles. • The 1D rod-like CuCo 2 O 4 with oxygen vacancies was obtained by morphology modulation. • A mechanism for the directional growth of NH 3 -induced Cu-Co precursors was proposed. • CCO/PPy exhibited enriched active sites with superior CRR and CER performance. • A high areal capacity of 31.3 mAh·cm −2 and over 400 cycles were achieved.

Molybdenum Disulfide/Tin Disulfide Ultrathin Nanosheets as Cathodes for Sodium-Carbon Dioxide Batteries.

Metal-CO2 rechargeable batteries are of great importance due to their higher energy density and carbon capture capability. In particular, Na-CO2 batteries are potential energy-storage devices that can replace Li-based batteries due to their lower cost and abundance. However, because of the slow electrochemical processes owing to the carbonated discharge products, the cell shows a high overpotential. The charge overpotential of the Na-CO2 battery increases because of the cathode catalyst's inability to break down the insulating discharge product Na2CO3, thereby resulting in poor cycle performance. Herein, we develop an ultrathin nanosheet MoS2/SnS2 cathode composite catalyst for Na-CO2 battery application. Insertion of SnS2 reduces the overpotential and improves the cyclic stability compared to pristine MoS2. As shown by a cycle test with a restricted capacity of 500 mAh/g at 50 mA/g, the battery is stable up to 100 discharge-charge cycles as the prepared catalyst successfully decomposes Na2CO3. Furthermore, the battery with the MoS2/SnS2 cathode catalyst has a discharge capacity of 35 889 mAh/g. The reasons for improvements in the cycle performance and overpotential of the MoS2/SnS2 composite cathode catalyst are examined by a combination of Raman, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure analysis, which reveals an underneath phase transformation and changes in the local atomic environment to be responsible. SnS2 incorporation induces S-vacancies in the basal plane and 1T character in 2H MoS2. This combined impact of SnS2 incorporation results in undercoordinated Mo atoms. Such a change in the electronic structure and the phase of the MoS2/SnS2 composite cathode catalyst results in higher catalytic activity and reduces the cell overpotential.

Forging Inspired Processing of Sodium‐Fluorinated Graphene Composite as Dendrite‐Free Anode for Long‐Life Na–CO2 Cells

Na–CO2 batteries recently are emerging as promising energy‐storage devices due to the abundance of Na in the earth's crust and the clean utilization of greenhouse gas CO2. However, similar to metallic Li, metallic Na also suffers from a serious issue of dendrite growth upon repeated cycling, while a facile method to solve this issue is still lacking. In this work, we report an effective, environmentally friendly method to inhibit Na dendrite growth by in situ constructing a stable, NaF‐rich solid electrolyte interface (SEI) layer on metallic Na via adding a small amount (~3 wt%) of fluorinated graphene (FG) in bulk Na. Inspired by the forging processing, a uniform Na/FG composite was obtained by melting and repetitive FG‐adsorbing/hammering processes. The Na/FG–Na/FG half cell exhibits a low voltage hysteresis of 110–140 mV over 700 h at a current density up to 5 mA cm−2 with an areal capacity as high as 5 mAh cm−2. Na–CO2 full cell with the Na/FG anode is able to sustain a stable cycling of 391 cycles at a limited capacity of 1000 mAh g−1. Long cycle life of the cell can be attributed to the protecting effect of the in situ fabricated NaF‐rich SEI layer on metallic Na. Both experiments and density functional theory (DFT) calculations confirm the formation of the NaF‐rich SEI layer. The inhibition effect of the NaF‐rich SEI layer for Na dendrites is verified by in situ optical microscopy observations.