Progress in research on Li–CO2 batteries: Mechanism, catalyst and performance

Regulating the Local Spin States in Spinel Oxides to Promote the Activity of Li-CO2 Batteries

Due to the high energy barrier, slow reaction kinetics, and complex reaction environments of Li-CO2 batteries, the development of durable and efficient catalysts is essential. Transition metal oxides are promising for their availability, stability, and 3d electronic features, with spin states playing an important role in CO2 activation. In this study, the local spin states are regulated by incorporating Ni into Co3O4 and its impact on activity in Li-CO2 batteries is explored. The results show that Ni atoms with high spin states in Ni0.1Co2.9O4 facilitate electron transfer from the catalyst to the unoccupied orbitals of CO2, providing sufficient active sites for the nucleation and growth of small Li2CO3 crystals. These small crystals have a low decomposition barrier, leading to improved battery efficiency. Therefore, Ni0.1Co2.9O4 shows superior catalytic performance with an overpotential of 0.72 V and an energy efficiency of ≈70% after 500 h. This work provides insights into the relationship between spin states and CO2 reactions, highlighting a promising avenue for developing high-performance metal-CO2 batteries.

Mechanistic understanding of CO2 reduction and evolution reactions in Li-CO2 batteries

Rechargeable Li-CO2 batteries have attracted extensive attention owing to their high theoretical energy density (1876 W h Kg-1). However, their practical application is hindered by large polarization, low coulombic efficiency, and cathode degradation. The electrochemical performance of Li-CO2 batteries is significantly affected by the thermodynamic stability and reaction kinetics of discharge products. Although advances have been achieved in cathode design and electrolyte optimization over the past decade, the reaction mechanism of the CO2 cathode has not yet been clear. In this review, various reaction mechanisms of CO2 reduction and evolution at the cathode interface are discussed, including different reaction routes under mixed O2/CO2 and pure CO2 environments. Furthermore, the regulating strategies of different discharge products, including Li2CO3, Li2C2O6, and Li2C2O4, are summarized to decrease the polarization and improve the cycling performance of Li-CO2 batteries. Finally, the challenges and perspectives are discussed from three aspects: reaction mechanisms, cathode catalysts, and electrolyte engineering, offering insights for the development of Li-CO2 batteries in the future.

Thermoplastic Polyurethane Derived from CO2 for the Cathode Binder in Li-CO2 Battery

High-energy-density Li-CO2 batteries are promising candidates for large-capacity energy storage systems. However, the development of Li-CO2 batteries has been hindered by low cycle life and high overpotential. In this study, we propose a CO2-based thermoplastic polyurethane (CO2-based TPU) with CO2 adsorption properties and excellent self-healing performance to replace traditional polyvinylidene fluoride (PVDF) as the cathode binder. The CO2-based TPU enhances the interfacial concentration of CO2 at the cathode/electrolyte interfaces, effectively increasing the discharge voltage and lowering the charge voltage of Li-CO2 batteries. Moreover, the CO2 fixed by urethane groups (-NH-COO-) in the CO2-based TPU are difficult to shuttle to and corrode the Li anode, minimizing CO2 side reactions with lithium metal and improving the cycling performance of Li-CO2 batteries. In this work, Li-CO2 batteries with CO2-based TPU as the multifunctional binders exhibit stable cycling performance for 52 cycles at a current density of 0.2 A g-1, with a distinctly lower polarization voltage than PVDF bound Li-CO2 batteries.

Revealing the CO2 Conversion at Electrode/Electrolyte Interfaces in Li-CO2 Batteries via Nanoscale Visualization Methods

Lithium-carbon dioxide (Li-CO2 ) battery technology presents a promising opportunity for carbon capture and energy storage. Despite tremendous efforts in Li-CO2 batteries, the complex electrode/electrolyte/CO2 triple-phase interfacial processes remain poorly understood, in particular at the nanoscale. Here, using in situ atomic force microscopy and laser confocal microscopy-differential interference contrast microscopy, we directly observed the CO2 conversion processes in Li-CO2 batteries at the nanoscale, and further revealed a laser-tuned reaction pathway based on the real-time observations. During discharge, a bi-component composite, Li2 CO3 /C, deposits as micron-sized clusters through a 3D progressive growth model, followed by a 3D decomposition pathway during the subsequent recharge. When the cell operates under laser (λ=405 nm) irradiation, densely packed Li2 CO3 /C flakes deposit rapidly during discharge. Upon the recharge, they predominantly decompose at the interfaces of the flake and electrode, detaching themselves from the electrode and causing irreversible capacity degradation. In situ Raman shows that the laser promotes the formation of poorly soluble intermediates, Li2 C2 O4 , which in turn affects growth/decomposition pathways of Li2 CO3 /C and the cell performance. Our findings provide mechanistic insights into interfacial evolution in Li-CO2 batteries and the laser-tuned CO2 conversion reactions, which can inspire strategies of monitoring and controlling the multistep and multiphase interfacial reactions in advanced electrochemical devices.

Recent Progress in Hot Spot Regulated Strategies for Catalysts Applied in Li-CO2 Batteries

As a high energy density power system, lithium-carbon dioxide (Li-CO2 ) batteries play an important role in addressing the fossil fuel crisis issues and alleviating the greenhouse effect. However, the sluggish transformation kinetic of CO2 and the difficult decomposition of discharge products impede the achievement of large capacity, small overpotential, and long life span of the batteries, which require exploring efficient catalysts to resolve these problems. In this review, the main focus is on the hot spot regulation strategies of the catalysts, which include the modulation of the active sites, the designing of microstructure, and the construction of composition. The recent progress of promising catalysis with hot spot regulated strategies is systematically addressed. Critical challenges are also presented and perspectives to provide useful guidance for the rational design of highly efficient catalysts for practical advanced Li-CO2 batteries are proposed.

Versatile Protein and Its Subunit Biomolecules for Advanced Rechargeable Batteries

Rechargeable batteries are of great significance for alleviating the growing energy crisis by providing efficient and sustainable energy storage solutions. However, the multiple issues associated with the diverse components in a battery system as well as the interphase problems greatly hinder their applications. Proteins and their subunits, peptides, and amino acids, are versatile biomolecules. Functional groups in different amino acids endow these biomolecules with unique properties including self-assembly, ion-conducting, antioxidation, great affinity to exterior species, etc. Besides, protein and its subunit materials can not only work in solid forms but also in liquid forms when dissolved in solutions, making them more versatile to realize materials engineering via diverse approaches. In this review, it is aimed to offer a comprehensive understanding of the properties of proteins and their subunits, and research progress of using these versatile biomolecules to address the engineering issues of various rechargeable batteries, including alkali-ion batteries, lithium-sulfur batteries, metal-air batteries, and flow batteries. The state-of-the-art advances in electrode, electrolyte, separator, binder, catalyst, interphase modification, as well as recycling of rechargeable batteries are involved, and the impacts of biomolecules on electrochemical properties are particularly emphasized. Finally, perspectives on this interesting field are also provided.

Porous Mo3 P/Mo Nanorods as Efficient Mott-Schottky Cathode Catalysts for Low Polarization Li-CO2 Battery

Li-CO2 battery with high energy density has aroused great interest recently, large-scale applications are hindered by the limited cathode catalysis performance and execrably cycle performance. Herein, Mo3 P/Mo Mott-Schottky heterojunction nanorod electrocatalyst with abundant porous structure is fabricated and served as cathodes for Li-CO2 batteries. The Mo3 P/Mo cathodes exhibit ultra-high discharge specific capacity of 10 577 mAh g-1 , low polarization voltage of 0.15 V, and high energy efficiency of up to 94.7%. Mott-Schottky heterojunction formed by Mo and Mo3 P drives electron transfer and optimizes the surface electronic structure, which is beneficial to accelerate the interface reaction kinetics. Distinctively, during the discharge process, the C2 O4 2- intermediates combine with Mo atoms to form a stable Mo-O coupling bridge on the catalyst surface, which effectively facilitate the formation and stabilization of Li2 C2 O4 products. In addition, the construction of the Mo-O coupling bridge between the Mott-Schottky heterojunction and Li2 C2 O4 promotes the reversible formation and decomposition of discharge products and optimizes the polarization performance of the Li-CO2 battery. This work provides another pathway for the development of heterostructure engineering electrocatalysts for high-performance Li-CO2 batteries.

Light-Assisted Metal-Air Batteries: Progress, Challenges, and Perspectives

Metal-air batteries are considered one of the most promising next-generation energy storage devices owing to their ultrahigh theoretical specific energy. However, sluggish cathode kinetics (O₂ and CO₂ reduction/evolution) result in large overpotentials and low round-trip efficiencies which seriously hinder their practical applications. Utilizing light to drive slow cathode processes has increasingly becoming a promising solution to this issue. Considering the rapid development and emerging issues of this field, this Review summarizes the current understanding of light-assisted metal-air batteries in terms of configurations and mechanisms, provides general design strategies and specific examples of photocathodes, systematically discusses the influence of light on batteries, and finally identifies existing gaps and future priorities for the development of practical light-assisted metal-air batteries.

Aprotic Lithium-Carbon Dioxide Batteries: Reaction Mechanism and Catalyst Design

In recent years, the combustion of fossil fuels leads to the release of a large amount of CO₂ gas, which induces the greenhouse effect and the energy crisis. To solve these problems, researchers have turned their focus to a novel Li-CO₂ battery (LCB). LCB has received much attention because of its high theoretical energy density and reversible CO₂ reduction/evolution process. So far, the emerging LCB still faces many challenges derived from the slow reaction kinetics of discharge products. In this review, the latest status and progress of LCB, especially the influence of the structure design of cathode catalysts on the battery performance, are systematically elaborated. This review summarizes in detail the existing issues and possible solutions of LCB, which is of high research value for further promoting the development of Li-Air battery.

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.

Redox Mediator-Enhanced Performance and Generation of Singlet Oxygen in Li-CO2 Batteries

Rechargeable Li-CO₂ batteries as a novel system developed in recent years directly use CO₂ as the reactant, which enables deeper penetration of energy storage and CO₂ utilization. The Li-CO₂ battery system, however, is at an early stage, and many challenges remained to be overcome urgently, especially the problem of high over-potential during the charging process. Here, we report a redox mediator, phenoxathiin, to assist the decomposition of Li₂CO₃ during the charging process, which effectively reduces the over-potential and improves the cycling performance of the battery. Furthermore, we detect the presence of singlet oxygen during the oxidation of Li₂CO₃ by phenoxathiin, which reveals more of the underlying science of the reaction mechanism of the Li-CO₂ battery.

A well-defined dual Mn-site based metal-organic framework to promote CO2 reduction/evolution in Li-CO2 batteries

A series of Li-CO2 battery cathode materials are reported based on metal-organic frameworks with dual-metal sites containing a metalloporphyrin and a metal-coordinated pyrazole. MnTPzP-Mn demonstrates a low voltage hysteresis of 1.05 V at 100 mA g-1 and good stability of 90 cycles at 200 mA g-1. Among them, the Mn-coordinated pyrazole site can promote the effective decomposition of Li2CO3, and the Mn-metalloporphyrin site contributes to the activation of CO2. This is the first example of using a crystalline cathode material with a well-defined structure to reveal natural catalytic sites for CO2 reduction/evolution reactions under aprotic conditions in Li-CO2 batteries.

Promoting the Performance of Li-CO2 Batteries via Constructing Three-Dimensional Interconnected K+ Doped MnO2 Nanowires Networks

Nowadays, Li–CO₂ batteries have attracted enormous interests due to their high energy density for integrated energy storage and conversion devices, superiorities of capturing and converting CO₂. Nevertheless, the actual application of Li–CO₂ batteries is hindered attributed to excessive overpotential and poor lifespan. In the past decades, catalysts have been employed in the Li–CO₂ batteries and been demonstrated to reduce the decomposition potential of the as-formed Li₂CO₃ during charge process with high efficiency. However, as a representative of promising catalysts, the high costs of noble metals limit the further development, which gives rise to the exploration of catalysts with high efficiency and low cost. In this work, we prepared a K⁺ doped MnO₂ nanowires networks with three-dimensional interconnections (3D KMO NWs) catalyst through a simple hydrothermal method. The interconnected 3D nanowires network catalysts could accelerate the Li ions diffusion, CO₂ transfer and the decomposition of discharge products Li₂CO₃. It is found that high content of K⁺ doping can promote the diffusion of ions, electrons and CO₂ in the MnO₂ air cathode, and promote the octahedral effect of MnO₆, stabilize the structure of MnO₂ hosts, and improve the catalytic activity of CO₂. Therefore, it shows a high total discharge capacity of 9,043 mAh g⁻¹, a low overpotential of 1.25 V, and a longer cycle performance.

Facile Synthesis of Birnessite δ-MnO2 and Carbon Nanotube Composites as Effective Catalysts for Li-CO2 Batteries

Li-CO₂ batteries are one type of promising energy storage and conversion devices to capture and utilize the greenhouse gas CO₂, mitigating global temperature rise and climate change. Catalysts that could effectively decompose the discharge product, Li₂CO₃, are essential for high-performance Li-CO₂ batteries. Benefiting from the interconnected porous structure, favorable oxygen vacancy, and the synergistic effects between the carbon nanotube (CNT) and layered birnessite δ-MnO₂, our Li-CO₂ cathodes with the as-prepared CNT@δ-MnO₂ catalyst can efficiently afford a large reaction surface area and abundant active sites, provide sufficient electron/Li⁺ transport pathways, and facilitate electrolyte infiltration and CO₂ diffusion, demonstrating low overpotential and superior cycling stability, which have been proven by both experimental characterization and theoretical computation. It is expected that this work can provide guidance for the design and synthesis of high-performance electrochemical catalysts for Li-CO₂ batteries.

Comparative Study of Li-CO2 and Na-CO2 Batteries with Ru@CNT as a Cathode Catalyst

Alkali metal-carbon dioxide (Li/Na-CO₂) batteries have generated widespread interest in the past few years owing to the attractive strategy of utilizing CO₂ while still delivering high specific energy densities. Among these systems, Na-CO₂ batteries are more cost effective than Li-CO₂ batteries because the former uses cheaper and abundant Na. Herein, a Ru/carbon nanotube (CNT) as a cathode material was used to compare the mechanisms, stabilities, overpotentials, and energy densities of Li-CO₂ and Na-CO₂ batteries. The potential of Na-CO₂ batteries as a viable energy storage technology was demonstrated.

RuO2-x decorated CoSnO3 nanoboxes as a high performance cathode catalyst for Li-CO2 batteries

Rechargeable Li-CO2 batteries contribute towards lessening fossil fuel depletion and alleviating the "greenhouse effect". However, more efforts must be made to figure out the critical problems of a high overpotential and poor cycling stability associated with this type of battery. Here, CoSnO3/RuO2-x nanocomposites were employed as an efficient air cathode for Li-CO2 batteries, which can lower the overpotential and improve their long-term cycling performance (around 145 cycles) remarkably.

Understanding Reaction Pathways in High Dielectric Electrolytes Using β-Mo2C as a Catalyst for Li-CO2 Batteries

The rechargeable Li-CO₂ battery has attracted considerable attention in recent years because of its carbon dioxide (CO₂) utilization and because it represents a practical Li-air battery. As with other battery systems such as the Li-ion, Li-O₂, and Li-S battery systems, understanding the reaction pathway is the first step to achieving high battery performance because the performance is strongly affected by reaction intermediates. Despite intensive efforts in this area, the effect of material parameters (e.g., the electrolyte, the cathode, and the catalyst) on the reaction pathway in Li-CO₂ batteries is not yet fully understood. Here, we show for the first time that the discharge reaction pathway of a Li-CO₂ battery composed of graphene nanoplatelets/beta phase of molybdenum carbide (GNPs/β-Mo₂C) is strongly influenced by the dielectric constant of its electrolyte. Calculations using the continuum solvents model show that the energy of adsorption of oxalate (C₂O₄^2-) onto Mo₂C under the low-dielectric electrolyte tetraethylene glycol dimethyl ether is lower than that under the high-dielectric electrolyte N,N-dimethylacetamide (DMA), indicating that the electrolyte plays a critical role in determining the reaction pathway. The experimental results show that under the high-dielectric DMA electrolyte, the formation of lithium carbonate (Li₂CO₃) as a discharge product is favorable because of the instability of the oxalate species, confirming that the dielectric properties of the electrolyte play an important role in the formation of the discharge product. The resulting Li-CO₂ battery exhibits improved battery performance, including a reduced overpotential and a remarkable discharge capacity as high as 14,000 mA h g^-1 because of its lower internal resistance. We believe that this work provides insights for the design of Li-CO₂ batteries with enhanced performance for practical Li-air battery applications.

Li-CO2 and Na-CO2 Batteries: Toward Greener and Sustainable Electrical Energy Storage

Metal-CO₂ batteries, especially Li-CO₂ and Na-CO₂ batteries, offer a novel and attractive strategy for CO₂ capture as well as energy conversion and storage with high specific energy densities. However, some scientific issues and challenges existing restrict their practical applications. Here, recent progress of crucial reaction mechanisms on cathodes in Li-CO₂ and Na-CO₂ batteries are summarized. The detailed reaction pathways can be modified by operation conditions, electrolyte compositions, and catalysts. Besides, specific discussions from aspects of catalyst design, stability of electrolytes, and anode protection are presented. Perspectives of several innovative directions are also put forward. This review provides an intensive understanding of Li-CO₂ and Na-CO₂ batteries and gives a useful guideline for the practical development of metal-CO₂ batteries and even metal-air batteries.

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 Li₂ CO₃ 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.

Preparation of RGO/TiO2/Ag Aerogel and Its Photodegradation Performance in Gas Phase Formaldehyde

To increase the utilization ratio and catalytic efficiency of the nano TiO2, The RGO/TiO2/(Ag) powders and RGO/TiO2/Ag aerogel photocatalyst were designed and prepared. The composition and microstructure of RGO/TiO2/(Ag) powders and RGO/TiO2/Ag aerogel were studied, in addition, the photocatalytic activity of RGO/TiO2/(Ag) powders and RGO/TiO2/Ag aerogel was researched by the photocatalytic degradation behavior of formaldehyde solution and formaldehyde gas respectively. The result indicate that TiO2 is uniformly loaded on the surface of RGO with a particle size of 10 nm to 20 nm. When the amount of graphene oxide added is 1 wt%, RGO/TiO2 powder has the highest degradation effect on formaldehyde solution, in addition, the introduction of Ag can greatly improve the photocatalytic effect of the sample. The results also show that the pore size of RGO/TiO2/Ag aerogel is between 7.6 nm and 12.1 nm, and the degradation rate of formaldehyde gas is 77.08% within 2 hours.

A Co-Doped MnO2 Catalyst for Li-CO2 Batteries with Low Overpotential and Ultrahigh Cyclability

Li-CO₂ batteries can not only capture CO₂ to solve the greenhouse effect but also serve as next-generation energy storage devices on the merits of economical, environmentally-friendly, and sustainable aspects. However, these batteries are suffering from two main drawbacks: high overpotential and poor cyclability, severely postponing the acceleration of their applications. Herein, a new Co-doped alpha-MnO₂ nanowire catalyst is prepared for rechargeable Li-CO₂ batteries, which exhibits a high capacity (8160 mA h g^-1 at a current density of 100 mA g^-1 ), a low overpotential (≈0.73 V), and an ultrahigh cyclability (over 500 cycles at a current density of 100 mA g^-1 ), exceeding those of Li-CO₂ batteries reported so far. The reaction mechanisms are interpreted depending on in situ experimental observations in combination with density functional theory calculations. The outstanding electrochemical properties are mostly associated with a high conductivity, a large fraction of hierarchical channels, and a unique Co interstitial doping, which might be of benefit for the diffusion of CO₂ , the reversibility of Li₂ CO₃ products, and the prohibition of side reactions between electrolyte and electrode. These results shed light on both CO₂ fixation and new Li-CO₂ batteries for energy storage.

A Highly Reversible Long-Life Li-CO2 Battery with a RuP2 -Based Catalytic Cathode

Rechargeable Li-CO₂ batteries have attracted worldwide attention due to the capability of CO₂ capture and superhigh energy density. However, they still suffer from poor cycling performance and huge overpotential. Thus, it is essential to explore highly efficient catalysts to improve the electrochemical performance of Li-CO₂ batteries. Here, phytic acid (PA)-cross-linked ruthenium complexes and melamine are used as precursors to design and synthesize RuP₂ nanoparticles highly dispersed on N, P dual-doped carbon films (RuP₂ -NPCFs), and the obtained RuP₂ -NPCF is further applied as the catalytic cathode for Li-CO₂ batteries. RuP₂ nanoparticles that are uniformly deposited on the surface of NPCF show enhanced catalytic activity to decompose Li₂ CO₃ at low charge overpotential. In addition, the NPCF its with porous structure in RuP₂ -NPCF provides superior electrical conductivity, high electrochemical stability, and enough ion/electron and space for the reversible reaction in Li-CO₂ batteries. Hence, the RuP₂ -NPCF cathode delivers a superior reversible discharge capacity of 11951 mAh g^-1 , and achieves excellent cyclability for more than 200 cycles with low overpotentials (<1.3 V) at the fixed capacity of 1000 mAh g^-1 . This work paves a new way to design more effective catalysts for Li-CO₂ batteries.

Carbon Nanotube@RuO2 as a High Performance Catalyst for Li-CO2 Batteries

Efficient electrocatalysts for Li₂CO₃ decomposition play an important role in Li-CO₂ batteries. In this paper, carbon nanotubes (CNTs) decorated with RuO₂ is firstly introduced as cathode materials for Li-CO₂ batteries. The CNT@RuO₂ composite can not only deliver a high specific capacity but also a lower charge voltage. With the CNT@RuO₂ cathodes, the Coulombic efficiency still remains around 100% until the 15th cycle. The charge voltage of early 30 cycles at a current of 50 mA·g^-1 with a capacity limit of 500 mAh·g^-1 can be fully lowered under 4.0 V. Particularly, the CNT@RuO₂ cathode can realize most decomposition of prefilled Li₂CO₃ and show a platform at around 3.9 V. This catalytic activity toward both in situ formed and preloaded Li₂CO₃ is more feasible for practical application in complex environment.

Conjugated Cobalt Polyphthalocyanine as the Elastic and Reprocessable Catalyst for Flexible Li-CO2 Batteries

Li-CO₂ batteries represent an attractive solution for electrochemical energy storage by utilizing atmospheric CO₂ as the energy carrier. However, their practical viability critically depends on the development of efficient and low-cost cathode catalysts for the reversible formation and decomposition of Li₂ CO₃ . Here, the great potential of a structurally engineered polymer is demonstrated as the cathode catalyst for rechargeable Li-CO₂ batteries. Conjugated cobalt polyphthalocyanine is prepared via a facile microwave heating method. Due to the crosslinked network, it is intrinsically elastic and has improved chemical, physical, and mechanical stability. Electrochemical measurements show that cobalt polyphthalocyanine facilitates the reversible formation and decomposition of Li₂ CO₃ , and therefore enables high-performance Li-CO₂ batteries with large areal capacity and impressive cycling performance. In addition, the elastic and reprocessable property of the polymeric catalyst renders it possible to fabricate flexible batteries.

Nanostructured Anatase Titania as a Cathode Catalyst for Li-CO2 Batteries

Lithium-carbon dioxide (Li-CO₂) batteries have garnered significant interest over the past 5 years as next-generation energy storage devices. In this article, we report a nanocomposite of anatase titania nanoparticles (TiO₂-NPs), carbon nanotubes, and carbon nanofibers as a freestanding gas diffusion cathode for Li-CO₂ batteries. Nanostructured anatase TiO₂ is demonstrated as a low-cost, easy-to-synthesize catalyst for CO₂ capture and utilization. With the developed composite electrode, we confirm the successful reversibility of the carbon dioxide reduction reaction and evolution reaction at the cathode and demonstrate improved Li-CO₂ cell performance through a variety of materials and electrochemical characterization techniques.

Fabricating Ir/C Nanofiber Networks as Free-Standing Air Cathodes for Rechargeable Li-CO2 Batteries

Li-CO₂ batteries are promising energy storage systems by utilizing CO₂ at the same time, though there are still some critical barriers before its practical applications such as high charging overpotential and poor cycling stability. In this work, iridium/carbon nanofibers (Ir/CNFs) are prepared via electrospinning and subsequent heat treatment, and are used as cathode catalysts for rechargeable Li-CO₂ batteries. Benefitting from the unique porous network structure and the high activity of ultrasmall Ir nanoparticles, Ir/CNFs exhibit excellent CO₂ reduction and evolution activities. The Li-CO₂ batteries present extremely large discharge capacity, high coulombic efficiency, and long cycling life. Moreover, free-standing Ir/CNF films are used directly as air cathodes to assemble Li-CO₂ batteries, which show high energy density and ultralong operation time, demonstrating great potential for practical applications.

Tailoring the components and morphology of discharge products towards highly rechargeable Li–CO/CO2 batteries

Herein, a new Li–CO/CO₂ battery system with high capacity, superior round-trip efficiency and excellent cycling stability is proposed.

Monodispersed Ru Nanoparticles Functionalized Graphene Nanosheets as Efficient Cathode Catalysts for O2-Assisted Li-CO2 Battery

In Li-CO₂ battery, due to the highly insulating nature of the discharge product of Li₂CO₃, the battery needs to be charged at a high charge overpotential, leading to severe cathode and electrolyte instability and hence poor battery cycle performance. Developing efficient cathode catalysts to effectively reduce the charge overpotential represents one of key challenges to realize practical Li-CO₂ batteries. Here, we report the use of monodispersed Ru nanoparticles functionalized graphene nanosheets as cathode catalysts in Li-CO₂ battery to significantly lower the charge overpotential for the electrochemical decomposition of Li₂CO₃. In our battery, a low charge voltage of 4.02 V, a high Coulomb efficiency of 89.2%, and a good cycle stability (67 cycles at a 500 mA h/g limited capacity) are achieved. It is also found that O₂ plays an essential role in the discharge process of the rechargeable Li-CO₂ battery. Under the pure CO₂ environment, Li-CO₂ battery exhibits negligible discharge capacity; however, after introducing 2% O₂ (volume ratio) into CO₂, the O₂-assisted Li-CO₂ battery can deliver a high capacity of 4742 mA h/g. Through an in situ quantitative differential electrochemical mass spectrometry investigation, the final discharge product Li₂CO₃ is proposed to form via the reaction 4Li⁺ + 2CO₂ + O₂ + 4e^- → 2Li₂CO₃. Our results validate the essential role of O₂ and can help deepen the understanding of the discharge and charge reaction mechanisms of the Li-CO₂ battery.

Highly Rechargeable Lithium-CO2 Batteries with a Boron- and Nitrogen-Codoped Holey-Graphene Cathode

Metal-air batteries, especially Li-air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO₂ (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li₂ CO₃ , making the battery less rechargeable. To make the Li-CO₂ batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO₂ reduction and evolution reactions and investigate the electrochemical behavior of Li-CO₂ batteries. Here, we demonstrate a rechargeable Li-CO₂ battery with a high reversibility by using B,N-codoped holey graphene as a highly efficient catalyst for CO₂ reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as-prepared Li-CO₂ batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long-term cycling stability over 200 cycles at a high current density of 1.0 A g^-1 . Our results open up new possibilities for the development of long-term Li-air batteries reusable under ambient conditions, and the utilization and storage of CO₂ .