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.     

Polymer-Based Batteries—Flexible and Thin Energy Storage Systems

Batteries have become an integral part of everyday life—from small coin cells to batteries for mobile phones, as well as batteries for electric vehicles and an increasing number of stationary energy storage applications. There is a large variety of standardized battery sizes (e.g., the familiar AA-battery or AAA-battery). Interestingly, all these battery systems are based on a huge number of different cell chemistries depending on the application and the corresponding requirements. There is not one single battery type fulfilling all demands for all imaginable applications. One battery class that has been gaining significant interest in recent years is polymer-based batteries. These batteries utilize organic materials as the active parts within the electrodes without utilizing metals (and their compounds) as the redox-active materials. Such polymer-based batteries feature a number of interesting properties, like high power densities and flexible batteries fabrication, among many more.     

Mo2N–ZrO2 Heterostructure Engineering in Freestanding Carbon Nanofibers for Upgrading Cycling Stability and Energy Efficiency of Li–CO2 Batteries

Li–CO₂ batteries have attracted considerable attention for their advantages of CO₂ fixation and high energy density. However, the sluggish dynamics of CO₂ reduction/evolution reactions restrict the practical application of Li–CO₂ batteries. Herein, a dual-functional Mo₂N–ZrO₂ heterostructure engineering in conductive freestanding carbon nanofibers (Mo₂N–ZrO₂@NCNF) is reported. The integration of Mo₂N–ZrO₂ heterostructure in porous carbons provides the opportunity to simultaneously accelerate electron transport, boost CO₂ conversion, and stabilize intermediate discharge product Li₂C₂O₄. Benefiting from the synchronous advantages, the Mo₂N–ZrO₂@NCNF catalyst endows the Li–CO₂ batteries with excellent cycle stability, good rate capability, and high energy efficiency even under high current densities. The designed cathodes exhibit an ultrahigh energy efficiency of 89.8% and a low charging voltage below 3.3 V with a potential gap of 0.32 V. Remarkably, stable operation over 400 cycles can be achieved even at high current densities of 50 µA cm⁻². This work provides valuable guidance for developing multifunctional heterostructured catalysts to upgrade longevity and energy efficiency of Li–CO₂ batteries.     

Porous Materials Applied in Nonaqueous Li–O2 Batteries: Status and Perspectives

Porous materials possessing high surface area, large pore volume, tunable pore structure, superior tailorability, and dimensional effect have been widely applied as components of lithium–oxygen (Li–O₂) batteries. Herein, the theoretical foundation of the porous materials applied in Li–O₂ batteries is provided, based on the present understanding of the battery mechanism and the challenges and advantageous qualities of porous materials. Furthermore, recent progress in porous materials applied as the cathode, anode, separator, and electrolyte in Li–O₂ batteries is summarized, together with corresponding approaches to address the critical issues that remain at present. Particular emphasis is placed on the importance of the correlation between the function-orientated design of porous materials and key challenges of Li–O₂ batteries in accelerating oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) kinetics, improving the electrode stability, controlling lithium deposition, suppressing the shuttle effect of the dissolved redox mediators, and alleviating electrolyte decomposition. Finally, the rational design and innovative directions of porous materials are provided for their development and application in Li–O₂ battery systems.     

Oxygen?Defect Enhanced Anion Adsorption Energy Toward Super?Rate and Durable Cathode for Ni–Zn Batteries

The alkaline zinc-based batteries with high energy density are becoming a research hotspot. However, the poor cycle stability and low-rate performance limit the...     

Electrical and physical properties of Na2O–CaO–MgO–SiO2 glass doped with NdF3

The structure of soda-calcia-magnesia-silicate glasses doped with rare-earth fluoride (NdF₃) was investigated by Fourier transform infrared spectrometer. The density and microhardness have been investigated in order to study the effect of doping NdF₃ on the physical properties of the studied glasses. The results showed that the density of glasses increases with the increase in NdF₃ contents. While, the increase of NdF₃ contents led to decrease the microhardness values of the studied samples. The AC electrical properties of samples were measured in the frequency interval 100 Hz up to 1 MHz. The increase of NdF₃ doping generally increases the conductivity and dielectric constants of the samples slightly. The obtained experimental data from samples were discussed based on the internal structure of the glass and the distribution of its constituents, connectivity and number of free charges or broken bonds.     

High Capacity Li2S–Li2O–LiI Positive Electrodes with Nanoscale Ion-Conduction Pathways for All-Solid-State Li/S Batteries

All-solid-state lithium–sulfur (Li/S) batteries are promising next-generation energy-storage devices owing to their high capacities and long cycle lives. The Li₂S active material used in the positive electrode has a high theoretical capacity; consequently, nanocomposites composed of Li₂S, solid electrolytes, and conductive carbon can be used to fabricate high-energy-density batteries. Moreover, the active material should be constructed with both micro- and nanoscale ion-conduction pathways to ensure high power. Herein, a Li₂S–Li₂O–LiI positive electrode is developed in which the active material is dispersed in an amorphous matrix. Li₂S–Li₂O–LiI exhibits high charge–discharge capacities and a high specific capacity of 998 mAh g⁻¹ at a 2 C rate and 25 °C. X-ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy observation suggest that Li₂O–LiI provides nanoscale ion-conduction pathways during cycling that activate Li₂S and deliver large capacities; it also exhibits an appropriate onset oxidation voltage for high capacity. Furthermore, a cell with a high areal capacity of 10.6 mAh cm^–2 is demonstrated to successfully operate at 25 °C using a Li₂S–Li₂O–LiI positive electrode. This study represents a major step toward the commercialization of all-solid-state Li/S batteries.     

Regulating the Electronic Structure of Bismuth Nanosheets by Titanium Doping to Boost CO2 Electroreduction and Zn–CO2 Batteries

The electrochemical carbon dioxide reduction reaction (E-CO₂RR) to formate is a promising strategy for mitigating greenhouse gas emissions and addressing the global energy crisis. Developing low-cost and environmentally friendly electrocatalysts with high selectivity and industrial current densities for formate production is an ideal but challenging goal in the field of electrocatalysis. Herein, novel titanium-doped bismuth nanosheets (Ti Bi NSs) with enhanced E-CO₂RR performance are synthesized through one-step electrochemical reduction of bismuth titanate (Bi₄Ti₃O₁₂). We comprehensively evaluated Ti Bi NSs using in situ Raman spectra, finite element method, and density functional theory. The results indicate that the ultrathin nanosheet structure of Ti Bi NSs can accelerate mass transfer, while the electron-rich properties can accelerate the production of *CO₂⁻ and enhance the adsorption strength of *OCHO intermediate. The Ti Bi NSs deliver a high formate Faradaic efficiency (FE_formate) of 96.3% and a formate production rate of 4032 µmol h⁻¹ cm⁻² at −1.01 V versus RHE. An ultra-high current density of −338.3 mA cm⁻² is achieved at −1.25 versus RHE, and simultaneously FE_formate still reaches more than 90%. Furthermore, the rechargeable Zn–CO₂ battery using Ti Bi NSs as a cathode catalyst achieves a maximum power density of 1.05 mW cm⁻² and excellent charging/discharging stability of 27 h.     

Electrical conductivity studies of Bi2O3–Li2O–ZnO–B2O3 glasses

Ac conductivity measurements and its analysis has been performed on xBi₂O₃–(65?x)Li₂O–20ZnO–15B₂O₃ (0 ≤ x ≤ 20) glasses in the temperature range 30–300 °C and a frequency range of 100 Hz to 1 MHz. The dc conductivity increased and the activation energy decreased with lithium content. The frequency dependent conductivity has been analyzed employing conductivity and modulus formalisms. The onset of conductivity relaxation shifts towards higher frequencies with temperature. The Almond–West conductivity formalism is used to explain the scaling behavior, and the relaxation mechanism is independent of temperature.     

High-Performance Biodegradable Energy Storage Devices Enabled by Heterostructured MoO3–MoS2 Composites

Biodegradable implantable devices are of growing interest in biosensors and bioelectronics. One of the key unresolved challenges is the availability of power supply. To enable biodegradable energy-storage devices, herein, 2D heterostructured MoO₃–MoS₂ nanosheet arrays are synthesized on water-soluble Mo foil, showing a high areal capacitance of 164.38 mF cm⁻² (at 0.5 mA cm⁻²). Employing the MoO₃–MoS₂ composite as electrodes of a symmetric supercapacitor, an asymmetric Zn-ion hybrid supercapacitor, and an Mg primary battery are demonstrated. Benefiting from the advantages of MoO₃–MoS₂ heterostructure, the Zn-ion hybrid supercapacitors deliver a high areal capacitance (181.86 mF cm⁻² at 0.5 mA cm⁻²) and energy density (30.56 µWh cm⁻²), and the Mg primary batteries provide a stable high output voltage (≈1.6 V) and a long working life in air/liquid environment. All of the used materials exhibit desirable biocompatibility, and these fabricated devices are also fully biodegradable. Demonstration experiments display their potential applications as biodegradable power sources for various electronic devices.     

A Carbon-Free and Free-Standing Cathode From Mixed-Phase TiO2 for Photo-Assisted Li–CO2 Battery

Li–CO₂ battery provides a new strategy to simultaneously solve the problems of energy storage and greenhouse effect. However, the severe polarization of CO₂ reduction and CO₂ evolution reaction impede the practical application. Herein, anodic TiO₂ nanotube arrays are first introduced as carbon-free and free-standing cathode for photo-assisted Li–CO₂ battery, and the photo-assisted charge and discharge mechanism is first clarified from the perspective of photocatalysis. Mixed-phase TiO₂ exhibits a long cycling life of 580 h (52 cycles) at 0.025 mA cm⁻² and delivers a high discharge specific capacity of 3001 µAh cm⁻² under UV illumination. The charge voltage dramatically reduces from 4.53 to 3.03 V under UV illumination. The improvement of photo-assisted Li–CO₂ battery performance relies on the synergistic effect of the hierarchical porous structure, strong UV absorption, efficient separation, and transfer of photo-generated electrons and holes at hetero-phase junction, and the facilitation of photo-generated electrons and holes on CO₂ reduction and CO₂ evolution reaction. This work can provide useful guidance for designing efficient photocathode for photo-assisted Li–CO₂ battery and other metal–air batteries.     

Sulfide-Based All-Solid-State Lithium–Sulfur Batteries:Challenges and Perspectives

Lithium–sulfur batteries with liquid electrolytes have been obstructed by severe shuttle effects and intrinsic safety concerns.Introducing inorganic solid-state electrolytes into lithium–sulfur systems is believed as an effective approach to eliminate these issues without sacrificing the high-energy density,which determines sulfidebased all-solid-state lithium–sulfur batteries.However,the lack of design principles for high-performance composite sulfur cathodes limits their further application.Th...     

Decoupled Solar Energy Storage and Dark Photocatalysis in a 3D Metal–Organic Framework

Materials enabling solar energy conversion and long-term storage for readily available electrical and chemical energy are key for off-grid energy distribution. Herein, the specific confinement of a rhenium coordination complex in a metal–organic framework (MOF) unlocks a unique electron accumulating property under visible-light irradiation. About 15 C g_MOF⁻¹ of electric charges can be concentrated and stored for over four weeks without loss. Decoupled, on-demand discharge for electrochemical reactions and H₂ evolution catalysis is shown and light-driven recharging can be conducted for >10 cycles with ≈90% of the initial charging capacity retained. Experimental investigations and theoretical calculations link electron trapping to MOF-induced geometry constraints as well as the coordination environment of the Re-center, highlighting the key role of MOF confinement on molecular guests. This study serves as the seminal report on 3D porous colloids achieving photoaccumulation of long-lived electrons, unlocking dark photocatalysis, and a path toward solar capacitor and solar battery systems.     

Introducing Hybrid Defects of Silicon Doping and Oxygen Vacancies into MOF-Derived TiO2–X@Carbon Nanotablets Toward High-Performance Sodium-Ion Storage

Titanium dioxide (TiO₂) is a promising anode material for sodium–ion batteries (SIBs), which suffer from the intrinsic sluggish ion transferability and poor conductivity. To overcome these drawbacks, a facile strategy is developed to synergistically engineer the lattice defects (i.e., heteroatom doping and oxygen vacancy generation) and the fine microstructure (i.e., carbon hybridization and porous structure) of TiO₂-based anode, which efficiently enhances the sodium storage performance. Herein, it is successfully realized that the Si-doping into the MIL-125 metal-organic framework structure, which can be easily converted to SiO₂/TiO_2–x@C nanotablets by annealing under inert atmosphere. After NaOH etching SiO₂/TiO_2–x@C which contains unbonded SiO₂ and chemically bonded Si O Ti, thus the lattice Si-doped TiO_2–x@C (Si-TiO_2–x@C) nanotablets with rich Ti³⁺/oxygen vacancies and abundant inner pores are developed. When examined as an anode for SIB, the Si-TiO_2–x@C exhibits a high sodium storage capacity (285 mAh g⁻¹ at 0.2 A g⁻¹), excellent long-term cycling, and high-rate performances (190 mAh g⁻¹ at 2 A g⁻¹ after 2500 cycles with 95.1% capacity retention). Theoretical calculations indicate that the rich Ti³⁺/oxygen vacancies and Si-doping synergistically contribute to a narrowed bandgap and lower sodiation barrier, which thus lead to fast electron/ion transfer coefficients and the predominant pseudocapacitive sodium storage behavior.     

Phase Relations in the Na2CO3–ZrO2–SiO2–H2O System at 0.1 and 0.05 GPa and 450°C

The phase relations in the Na₂CO₃–ZrO₂–SiO₂–H₂O system were studied at 0.1 and 0.05 GPa and 450°C using large-particle-size and nanocrystalline zirconias. Four silicates were obtained when use was made of readily soluble ZrO₂(nanocr): ZrSiO₄, Na₂ZrSi₆O₁₅ · 3H₂O, Na₂ZrSi₃O₉ · 2H₂O, and Na₄Zr₂Si₅O₁₆ · H₂O. In the system containing poorly soluble ZrO₂(cr), only Na₂ZrSi₆O₁₅ · 3H₂O was found to crystallize. It is shown that the structures of all the Na–Zr silicates contain invariant six-polyhedron structural precursors, each made up of two ZrO₆ octahedra and four SiO₄ tetrahedra, and belong to a homologous series of structures based on the silicate Na₂ZrSi₂O₇, which forms via direct packing of cyclic subpolyhedral precursors.     

Electrical behaviour of La1.33−xM3xTi2O6 perovskites (M=Li,Na and K)

Structural characterization and ionic conductivity properties of the La_1.33−xM_3xTi₂O₆ (M=Li, Na and K) perovskite-type series are reported. From X-Ray diffraction data two different symmetries, tetragonal and orthorhombic, were observed as a function of the ionic size of alkaline cations as well as their proportion in the compounds. Crystallographic features seem to influence on the two possible conduction mechanisms. Orthorhombic samples allow the charge carriers motion through a 3D pathway whereas in the tetragonal ones mobile cations only can move into the A-planes in which are located.     

Tailoring the Spatial Distribution and Content of Inorganic Nitrides in Solid–Electrolyte Interphases for the Stable Li Anode in Li–S Batteries

Among the alternatives to lithium-ion batteries, lithium–sulfur(Li–S)batteries are considered as an attractive option because of their high theoretical energy density of 2570 Wh kg^-1. However, the application of the Li–S battery has been plagued by the rapid failure of the Li anode due to the Li dendrite growth and severe parasitic reactions between Li and lithium polysulfides. The physicochemical properties of the solid–electrolyte interphase have a profound impact on the performance...     

Gas Diffusion Strategy for Inserting Atomic Iron Sites into Graphitized Carbon Supports for Unusually High-Efficient CO2 Electroreduction and High-Performance Zn–CO2 Batteries

Emerging single-atom catalysts (SACs) hold great promise for CO₂ electroreduction (CO₂ER)_, but the design of highly active and cost-efficient SACs is still challenging. Herein, a gas diffusion strategy, along with one-step thermal activation, for fabricating N-doped porous carbon polyhedrons with trace isolated Fe atoms (Fe₁NC) is developed. The optimized Fe₁NC/S₁-1000 with atomic Fe-N₃ sites supported by N-doped graphitic carbons exhibits superior CO₂ER performance with the CO Faradaic efficiency up to 96% at −0.5 V, turnover frequency of 2225 h⁻¹, and outstanding stability, outperforming almost all previously reported SACs based on N-doped carbon supported nonprecious metals. The observed excellent CO₂ER performance is attributed to the greatly enhanced accessibility and intrinsic activity of active centers due to the increased electrochemical surface area through size modulation and the redistribution of doped N species by thermal activation. Experimental observations and theoretical calculations reveal that the Fe-N₃ sites possess balanced adsorption energies of *COOH and *CO intermediates, facilitating CO formation. A universal gas diffusion strategy is used to exclusively yield a series of dimension-controlled carbon-supported SACs with single Fe atoms while a rechargeable Zn–CO₂ battery with Fe₁NC/S₁-1000 as cathode is developed to deliver a maximal power density of 0.6 mW cm⁻².     

High-Performance,Long-Life,Rechargeable Li–CO2 Batteries based on a 3D Holey Graphene Cathode Implanted with Single Iron Atoms

A highly efficient cathode catalyst for rechargeable Li–CO₂ batteries is successfully synthesized by implanting single iron atoms into 3D porous carbon architectures, consisting of interconnected N,S-codoped holey graphene (HG) sheets. The unique porous 3D hierarchical architecture of the catalyst with a large surface area and sufficient space within the interconnected HG framework can not only facilitate electron transport and CO₂/Li⁺ diffusion, but also allow for a high uptake of Li₂CO₃ to ensure a high capacity. Consequently, the resultant rechargeable Li–CO₂ batteries exhibit a low potential gap of ≈1.17 V at 100 mA g⁻¹ and can be repeatedly charged and discharged for over 200 cycles with a cut-off capacity of 1000 mAh g⁻¹ at a high current density of 1 A g⁻¹. Density functional theory calculations are performed and the observed appealing catalytic performance is correlated with the hierarchical structure of the carbon catalyst. This work provides an effective approach to the development of highly efficient cathode catalysts for metal–CO₂ batteries and beyond.