Exploiting Synergistic Effect by Integrating Ruthenium–Copper Nanoparticles Highly Co‐Dispersed on Graphene as Efficient Air Cathodes for Li–CO2 Batteries

Li–CO₂ batteries are attractive electrical energy storage devices; however, they still suffer from unsatisfactory electrochemical performance, and the kinetics of CO₂ reduction and evolution reactions must be improved significantly. Herein, a composite of ruthenium–copper nanoparticles highly co‐dispersed on graphene (Ru–Cu–G) as efficient air cathodes for Li–CO₂ batteries is designed. The Li–CO₂ batteries with Ru–Cu–G cathodes exhibit ultra‐low overpotential and can be operated for 100 cycles with a fixed capacity of 1000 mAh g^?1 at 200 and 400 mA g^?1. The synergistic effect between Ru and Cu not only regulates the growth of discharge products, but also promotes CO₂ reduction and evolution reactions by changing the electron cloud density of the surface between Ru and Cu. This work may provide new directions and strategies for developing highly efficient air cathodes for Li–CO₂ batteries, or even practical Li–air batteries.     

Realizing Interfacial Electronic Interaction within ZnS Quantum Dots/N‐rGO Heterostructures for Efficient Li–CO2 Batteries

With high theoretical energy density, rechargeable metal–gas batteries (e.g., Li–CO₂ battery) are considered as one of the most promising energy storage devices. However, their practical applications are hindered by the sluggish reaction kinetics and discharge product accumulation during battery cycling. Currently, the solutions focus on exploration of new catalysts while the thorough understanding of their underlying mechanisms is often ignored. Herein, the interfacial electronic interaction within rationally designed catalysts, ZnS quantum dots/nitrogen‐doped reduced graphene oxide (ZnS QDs/N‐rGO) heterostructures, and their effects on transformation and deposition of discharge products in the Li–CO₂ battery are revealed. In this work, the interfacial interaction can both enhance the catalytic activities of ZnS QDs/N‐rGO heterostructures and induce the nucleation of discharge products to form a homogeneous Li₂CO₃/C film with excellent electronic transmission and high electrochemical activities. When the batteries cycle within a cutoff specific capacity of 1000 mAh g^?1 at a current density of 400 mA g^?1, the cycling performance of the Li–CO₂ battery using a ZnS QDs/N‐rGO cathode is over 3 and 9 times than those coupled with a ZnS nanosheets (NST)/N‐rGO cathode and a N‐rGO cathode, respectively. This work provides comprehensive understandings on designing catalysts for Li–CO₂ batteries as well as other rechargeable metal–gas batteries.     

Tailored Reaction Route by Micropore Confinement for Li–S Batteries Operating under Lean Electrolyte Conditions

Lithium‐sulfur (Li–S) batteries are one of the most promising alternative energy storage systems beyond Li‐ion batteries. However, the sluggish kinetics of the nucleation and growth of the solid discharge product of Li₂S/Li₂S₂ in the lower discharge plateau has been recently identified as a critical hurdle for attaining high specific capacity in Li–S batteries with high sulfur loadings under lean electrolyte conditions. Herein, a new strategy of breaking the charge‐transport bottleneck by successful generation of experimentally verified stable Li₂S₂ and a reservoir of quasi‐solid lithium polysulfides within the micropores of activated carbon fiber cloth as a high‐sulfur‐loading host is proposed. The developed Li–S cell is capable of delivering a highly sustainable areal capacity of 6.0 mAh cm^?2 under lower electrolyte to sulfur ratios (<3.0 mL_E g_S^?1). Micropore confinement leads to generation of solid Li₂S₂ that enables high utilization of the entire electroactive area by its inherent self‐healing capacity. This strategy opens a new avenue for rational material designs for Li–S batteries under lean electrolyte condition.     

Mechanistic Study Revealing the Role of the Br3−/Br2 Redox Couple in CO2‐Assisted Li–O2 Batteries

Replacing oxygen (O₂) with air is a critical step in the development of lithium (Li)–air batteries. A trace amount of carbon dioxide (CO₂) in the air is, however, influentially involved in the O₂ chemistry, which indicates that a fundamental understanding of the effect of CO₂ is required for the design of practical cells. When up to 30% CO₂ is added to Li–O₂ cells, CO₂ acts as an O₂^? scavenger. Their chemical reactions form soluble products, CO₄^2? and C₂O₆^2?, in the tetraglyme electrolyte solution, and enhance full capacity and cell cyclability. A critical challenge is, however, the sluggish decomposition of the coproduct Li₂CO₃ during recharge. To lower the charging overpotential, a Br₃^?/Br₂ redox couple is incorporated and its redox behavior is investigated using spectroscopic methods. The redox shuttle of Br₃^?/Br₂ decomposes amorphous Li₂CO₃ more efficiently than its crystalline counterpart. It is revealed that Br₂ combines with Br₃^? to form a Br₂···Br₃^? complex, which acts as a mobile catalyst in the electrolyte solution without swift precipitation of the nonpolar Br₂. This comprehensive study, revealing the molecular structure and redox process of mobile catalysts, provides an insight into improving the design of redox couples toward superior cycling performance.     

Metal Sulfide‐Decorated Carbon Sponge as a Highly Efficient Electrocatalyst and Absorbant for Polysulfide in High‐Loading Li2S Batteries

Owing to its high theoretical specific capacity (1166 mA h g^?1) and particularly its advantage to be paired with a lithium‐metal‐free anode, lithium sulfide (Li₂S) is regarded as a much safer cathode for next‐generation advanced lithium–sulfur (Li–S) batteries. However, the low conductivity of Li₂S and particularly the severe “polysulfide shuttle” of lithium polysulfide (LiPS) dramatically hinder their practical application in Li–S batteries. To address such issues, herein a bifuctional 3D metal sulfide‐decorated carbon sponge (3DTSC), which is constructed by 1D carbon nanowires cross‐linked with 2D graphene nanosheets with high conductivity and polar 0D metal sulfide nanodots with efficient electrocatalytic activity and strong chemical adsorption capability for LiPSs, is presented. Benefiting from the well‐designed multiscale, multidimensional 3D porous nanoarchitecture with high conductivity, and efficient electrocatalytic and absorption ability, the 3DTSC significantly mitigates LiPS shuttle, improves the utilization of Li₂S, and facilitates the transport of electrons and ions. As a result, even with a high Li₂S loading of 8 mg cm^?2, the freestanding 3DTSC‐Li₂S cathode without a polymer binder and metallic current collector delivers outstanding electrochemical performance with a high areal capacity of 8.44 mA h cm^?2.     

Unraveling the Dual Functionality of High‐Donor‐Number Anion in Lean‐Electrolyte Lithium‐Sulfur Batteries

Minimizing electrolyte use is essential to achieve high practical energy density of lithium–sulfur (Li–S) batteries. However, the sulfur cathode is more readily passivated under a lean electrolyte condition, resulting in low sulfur utilization. In addition, continuous electrolyte decomposition on the Li metal anode aggravates the problem, provoking rapid capacity decay. In this work, the dual functionalities of NO₃^? as a high‐donor‐number (DN) salt anion is presented, which improves the sulfur utilization and cycling stability of lean‐electrolyte Li–S batteries. The NO₃^? anion elevates the solubility of the sulfur species based on its high electron donating ability, achieving a high sulfur utilization of above 1200 mA h g^?1. Furthermore, the anion suppresses electrolyte decomposition on the Li metal by regulating the lithium ion (Li⁺) solvation sheath, enhancing the cycle performance of the lean electrolyte cell. By understanding the anionic effects, this work demonstrates the potential of the high‐DN electrolyte, which is beneficial for both the cathode and anode of Li–S batteries.     

From Lithium‐Oxygen to Lithium‐Air Batteries: Challenges and Opportunities

Lithium ‐ air batteries have become a focus of research on future battery technologies. Technical issues associated with lithium‐air batteries, however, are rather complex. Apart from the sluggish oxygen reaction kinetics which demand efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts, issues are also inherited from the nature of an open battery system and the use of reactive metal lithium as anode. Lithium‐air batteries, which exchange oxygen directly with ambient air, face more challenges due to the additional oxidative agents of moisture, carbon dioxide, etc. which degrade the metal lithium anode, deteriorating the performance of the batteries. In order to improve the cycling performance one must hold a full picture of lithium‐oxygen electrochemistry in the presence of carbon dioxide and/or moisture and fully understand the fundamentals of chemistry reactions therein. Recent advances in the exploration of the effect of moisture and CO₂ contaminants on Li‐O₂ batteries are reviewed, and the mechanistic understanding of discharge/charge process in O₂ at controlled level of moisture and/or CO₂ are illustrated. Prospects for development opportunities of Li‐air batteries, insight into future research directions, and guidelines for the further development of rechargeable Li‐air batteries are also given.     

Enhanced Cyclability of Lithium–Oxygen Batteries with Electrodes Protected by Surface Films Induced via In Situ Electrochemical Process

Although the rechargeable lithium–oxygen (Li–O₂) batteries have extremely high theoretical specific energy, the practical application of these batteries is still limited by the instability of their carbon‐based air‐electrode, Li metal anode, and electrodes, toward reduced oxygen species. Here a simple one‐step in situ electrochemical precharging strategy is demonstrated to generate thin protective films on both carbon nanotubes (CNTs), air‐electrodes and Li metal anodes simultaneously under an inert atmosphere. Li–O₂ cells after such pretreatment demonstrate significantly extended cycle life of 110 and 180 cycles under the capacity‐limited protocol of 1000 mA h g^?1 and 500 mA h g^?1, respectively, which is far more than those without pretreatment. The thin‐films formed from decomposition of electrolyte during in situ electrochemical precharging processes in an inert environment, can protect both CNTs air‐electrode and Li metal anode prior to conventional Li–O₂ discharge/charge cycling, where reactive reduced oxygen species are formed. This work provides a new approach for protection of carbon‐based air‐electrodes and Li metal anodes in practical Li–O₂ batteries, and may also be applied to other battery systems.     

An Efficient Separator with Low Li‐Ion Diffusion Energy Barrier Resolving Feeble Conductivity for Practical Lithium–Sulfur Batteries

Due to unprecedented features including high‐energy density, low cost, and light weight, lithium–sulfur batteries have been proposed as a promising successor of lithium‐ion batteries. However, unresolved detrimental low Li‐ion transport rates in traditional carbon materials lead to large energy barrier in high sulfur loading batteries, which prevents the lithium–sulfur batteries from commercialization. In this report, to overcome the challenge of increasing both the cycling stability and areal capacity, a metallic oxide composite (NiCo₂O₄@rGO) is designed to enable a robust separator with low energy barrier for Li‐ion diffusion and simultaneously provide abundant active sites for the catalytic conversion of the polar polysulfides. With a high sulfur‐loading of 6 mg cm^?2 and low sulfur/electrolyte ratio of 10, the assembled batteries deliver an initial capacity of 5.04 mAh cm^?2 as well as capacity retention of 92% after 400 cycles. The metallic oxide composite NiCo₂O₄@rGO/PP separator with low Li‐ion diffusion energy barrier opens up the opportunity for lithium–sulfur batteries to achieve long‐cycle, cost‐effective operation toward wide applications in electric vehicles and electronic devices.     

Surface‐Plasmon‐Assisted Photoelectrochemical Reduction of CO2 and NO3− on Nanostructured Silver Electrodes

Electrochemical reduction of carbon dioxide (CO₂) typically suffers from low selectivity and poor reaction rates that necessitate high overpotentials, which impede its possible application for CO₂ capture, sequestration, or carbon‐based fuel production. New strategies to address these issues include the utilization of photoexcited charge carriers to overcome activation barriers for reactions that produce desirable products. This study demonstrates surface‐plasmon‐enhanced photoelectrochemical reduction of CO₂ and nitrate (NO₃^?) on silver nanostructured electrodes. The observed photocurrent likely originates from a resonant charge transfer between the photogenerated plasmonic hot electrons and the lowest unoccupied molecular orbital (MO) acceptor energy levels of adsorbed CO₂, NO₃^?, or their reductive intermediates. The observed differences in the resonant effects at the Ag electrode with respect to electrode potential and photon energy for CO₂ versus NO₃^? reduction suggest that plasmonic hot‐carriers interact selectively with specific MO acceptor energy levels of adsorbed surface species such as CO₂, NO₃^?, or their reductive intermediates. This unique plasmon‐assisted charge generation and transfer mechanism can be used to increase yield, efficiency, and selectivity of various photoelectrochemical processes.     

Nature‐Inspired Tri‐Pathway Design Enabling High‐Performance Flexible Li–O2 Batteries

Trees have an abundant network of channels for the multiphase transport of water, ions, and nutrients. Recent studies have revealed that multiphase transport of ions, oxygen (O₂) gas, and electrons also plays a fundamental role in lithium–oxygen (Li–O₂) batteries. The similarity in transport behavior of both systems is the inspiration for the development of Li–O₂ batteries from natural wood featuring noncompetitive and continuous individual pathways for ions, O₂, and electrons. Using a delignification treatment and a subsequent carbon nanotube/Ru nanoparticle coating process, one is able to convert a rigid and electrically insulating wood membrane into a flexible and electrically conductive material. The resulting cell walls are comprised of cellulose nanofibers with abundant nanopores, which are ideal for Li⁺ ion transport, whereas the unperturbed wood lumina act as a pathway for O₂ gas transport. The noncompetitive triple pathway design endows the wood‐based cathode with a low overpotential of 0.85 V at 100 mA g^?1, a record‐high areal capacity of 67.2 mAh cm^?2, a long cycling life of 220 cycles, and superior electrochemical and mechanical stability. The integration of such excellent electrochemical performance, outstanding mechanical flexibility, and renewable yet cost‐effective starting materials via a nature‐inspired design opens new opportunities for developing portable energy storage devices.     

Interfacial Charge Field in Hierarchical Yolk–Shell Nanocapsule Enables Efficient Immobilization and Catalysis of Polysulfides Conversion

Inhibiting the shuttle effect of lithium polysulfides and accelerating their conversion kinetics are crucial for the development of high‐performance lithium–sulfur (Li–S) batteries. Herein, a modified template method is proposed to synthesize the robust yolk–shell sulfur host that is constructed by enveloping dispersive Fe₂O₃ nanoparticles within Mn₃O₄ nanosheet‐grafted hollow N‐doped porous carbon capsules (Fe₂O₃@N‐PC/Mn₃O₄‐S). When applied as a cathode for Li–S batteries, the as‐prepared Fe₂O₃@N‐PC/Mn₃O₄‐S can deliver capacities as high as 1122 mAh g^?1 after 200 cycles at 0.5 C and 639 mAh g^?1 after 1500 cycles at 10 C, respectively. Remarkably, even as the areal sulfur loading is increased to 5.1 mg cm^?2, the cathode can still maintain a high areal specific capacity of 5.08 mAh cm^?2 with a fading rate of only 0.076% per cycle over 100 cycles at 0.1 C. By a further combination analysis of electron holography and electron energy loss spectroscopy, the outstanding performance is revealed to be mainly traced to the oxygen‐vacancy‐induced interfacial charge field, which immobilizes and catalyzes the conversion of lithium polysulfides, assuring low polarization, fleet redox reaction kinetics, and sufficient utilization of sulfur. These new findings may shed light on the dependence of electrochemical performance on the heterostructure of sulfur hosts.     

Dense Graphene Monolith for High Volumetric Energy Density Li–S Batteries

Despite the outstanding gravimetric performance of lithium–sulfur (Li–S) batteries, their practical volumetric energy density is normally lower than that of lithium‐ion batteries, mainly due to the low density of nanostructured sulfur as well as the porous carbon hosts. Here, a novel approach is developed to fabricate high‐density graphene bulk materials with “ink‐bottle‐like” mesopores by phosphoric acid (H₃PO₄) activation. These pores can effectively confine the polysulfides due to their unique structure with a wide body and narrow neck, which shows only a 0.05% capacity fade per cycle for 500 cycles (75% capacity retention) for accommodating polysulfides. With a density of 1.16 g cm^?3, a hybrid cathode containing 54 wt% sulfur delivers a high volumetric capacity of 653 mA h cm^?3. As a result, a device‐level volumetric energy density as high as 408 W h L^?1 is achieved with a cathode thickness of 100 µm. This is a periodic yet practical advance to improve the volumetric performance of Li–S batteries from a device perspective. This work suggests a design principle for the real use Li–S batteries although there is a long way ahead to bridge the gap between Li–S batteries and Li–ion batteries in volumetric performance.     

MnMoO4 Electrocatalysts for Superior Long‐Life and High‐Rate Lithium‐Oxygen Batteries

Lithium‐oxygen batteries represent a significant scientific challenge for high‐rate and long‐term cycling using oxygen electrodes that contain efficient electrocatalysts. The mixed transition metal oxide catalysts provide the most efficient catalytic activity for partial heterogeneous surface cations with oxygen vacancies as the active phase. They include multiple oxidation states and oxygen vacancies. Here, using a combination of transmission electron microscopy, differential electrochemical mass spectrometry, X‐ray photoelectron spectroscopy, and electrochemical properties to probe the surface of the MnMoO₄ nanowires, it is shown that the intrinsic MnMoO₄ oxygen vacancies on the oxygen electrode are an effective strategy to achieve a high reversibility and high efficiency for lithium‐oxygen (Li‐O₂) batteries. The modified MnMoO₄ nanowires exhibit a highly stable capacity at a fixed capacity of 5000 mA h g_sp^?1 (calculated weight of Super P carbon black) during 50 cycles, a high‐rate capability at a current rate of 3000 mA g_sp^?1 during 70 cycles, and a long‐term reversible capacity during 188 cycles at a fixed capacity of 1000 mA h g_sp^?1. It is demonstrated that this strategy for creating mixed transition metal oxides (e.g., MnMoO₄) may pave the way for the new structural design of electrocatalysts for Li‐O₂ batteries.     

Mesoporous TiO2‐Sn/C Core‐Shell Nanowire Arrays as High‐Performance 3D Anodes for Li‐Ion Batteries

Three‐dimensional mesoporous TiO₂‐Sn/C core‐shell nanowire arrays are prepared on Ti foil as anodes for lithium‐ion batteries. Sn formed by a reduction of SnO₂ is encapsulated into TiO₂ nanowires and the carbon layer is coated onto it. For additive‐free, self‐supported anodes in Li‐ion batteries, this unique core‐shell composite structure can effectively buffer the volume change, suppress cracking, and improve the conductivity of the electrode during the discharge‐charge process, thus resulting in superior rate capability and excellent long‐term cycling stability. Specifically, the TiO₂‐Sn/C nanowire arrays display rechargeable discharge capacities of 769, 663, 365, 193, and 90 mA h g^?1 at 0.1C, 0.5C, 2C 10C, and 30C, respectively (1C = 335 mA g^?1). Furthermore, the TiO₂‐Sn/C nanowire arrays exhibit a capacity retention rate of 84.8% with a discharge capacity of over 160 mA h g^?1, even after 100 cycles at a high current rate of 10C.     

Superior CO2 Adsorption Capacity on N‐doped,High‐Surface‐Area,Microporous Carbons Templated from Zeolite

Zeolite‐templated, high‐surface‐area, microporous, N‐doped carbons exhibit the highest CO₂ uptake capacity recorded to date for any carbon material and one of the highest for any inorganic or organic porous material of up to 6.9 mmol g^?1 at 273 K and ambient pressure and 4.4 mmol g^?1 at ambient temperature and pressure, along with an initial CO₂ adsorption energy of 36 kJ mol^?1 at lower coverage and 20 kJ mol^?1 at higher CO₂ coverage. Combined with their ease of preparation, excellent recyclability and regeneration stability, and high selectivity for CO₂, the N‐doped zeolite‐templated carbons are amongst the most promising solid‐state absorbents reported so far for CO₂ capture and storage.     

An Improved Li–SeS2 Battery with High Energy Density and Long Cycle Life

Selenium–sulfur solid solutions are a class of potential cathode materials for high energy batteries, since they have higher theoretical capacities than selenium and improved conductivity over sulfur. Here, a high‐performance cathode material by confining 70 wt% of SeS₂ in a highly ordered mesoporous carbon (CMK‐3) framework with a polydopamine (PDA) protection sheath for novel Li–Se/S batteries is reported. With a relatively high SeS₂ mass loading of 2.6–3 mg cm^?2, the CMK‐3/SeS₂@PDA cathode exhibits a high capacity of >1200 mA h g^?1 at 0.2 A g^?1, excellent C‐rate capability of 535 mA h g^?1 at 5 A g^?1, and prolonged life over 500 cycles. Benefitting from the unique advantages of SeS₂ and the rationally designed host framework, this new cathode material demonstrates a feasible strategy to overcome the bottlenecks of current Li–S systems for high energy density rechargeable batteries.     

NiCo2O4 Nanofibers as Carbon‐Free Sulfur Immobilizer to Fabricate Sulfur‐Based Composite with High Volumetric Capacity for Lithium–Sulfur Battery

Both the energy density and cycle stability are still challenges for lithium–sulfur (Li–S) batteries in future practical applications. Usually, light‐weight and nonpolar carbon materials are used as the hosts of sulfur, however they struggle on the cycle stability and undermine the volumetric energy density of Li–S batteries. Here, heavy NiCo₂O₄ nanofibers as carbon‐free sulfur immobilizers are introduced to fabricate sulfur‐based composites. NiCo₂O₄ can accelerate the catalytic conversion kinetics of soluble intermediate polysulfides by strong chemical interaction, leading to a good cycle stability of sulfur cathodes. Specifically, the S/NiCo₂O₄ composite presents a high gravimetric capacity of 1125 mAh g^?1 at 0.1 C rate with the composite as active material, and a low fading rate of 0.039% per cycle over 1500 cycles at 1 C rate. In particular, the S/NiCo₂O₄ composite with the high tap density of 1.66 g cm^?3 delivers large volumetric capacity of 1867 mAh cm^?3, almost twice that of the conventional S/carbon composites.     

Fluorine‐Free Noble Salt Anion for High‐Performance All‐Solid‐State Lithium–Sulfur Batteries

Amongst post‐Li‐ion battery technologies, lithium–sulfur (Li–S) batteries have captured an immense interest as one of the most appealing devices from both the industrial and academia sectors. The replacement of conventional liquid electrolytes with solid polymer electrolytes (SPEs) enables not only a safer use of Li metal (Li°) anodes but also a flexible design in the shape of Li–S batteries. However, the practical implementation of SPEs‐based all‐solid‐state Li–S batteries (ASSLSBs) is largely hindered by the shuttling effect of the polysulfide intermediates and the formation of dendritic Li° during the battery operation. Herein, a fluorine‐free noble salt anion, tricyanomethanide [C(CN)₃^?, TCM^?], is proposed as a Li‐ion conducting salt for ASSLSBs. Compared to the widely used perfluorinated anions {e.g., bis(trifluoromethanesulfonyl)imide anion, [N(SO₂CF₃)₂)]^?, TFSI^?}, the LiTCM‐based electrolytes show decent ionic conductivity, good thermal stability, and sufficient anodic stability suiting the cell chemistry of ASSLSBs. In particular, the fluorine‐free solid electrolyte interphase layer originating from the decomposition of LiTCM exhibits a good mechanical integrity and Li‐ion conductivity, which allows the LiTCM‐based Li–S cells to be cycled with good rate capability and Coulombic efficiency. The LiTCM‐based electrolytes are believed to be the most promising candidates for building cost‐effective and high energy density ASSLSBs in the near future.     

Stabilization of Li Metal Anode in DMSO‐Based Electrolytes via Optimization of Salt–Solvent Coordination for Li–O2 Batteries

The conventional electrolyte of 1 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl sulfoxide (DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li–O₂ batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li–O₂ batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI^?)_a ? Li⁺? (DMSO)_b (where a + b = 4), and thus enhances their stability with Li metal anodes. In addition, such salt–solvent complexes have higher Gibbs activation energy barriers than the free DMSO solvent molecules, indicating improved stability of the electrolyte against the attack of superoxide radical anions. Therefore, the stability of this highly concentrated electrolyte at both Li metal anodes and carbon‐based air electrodes has been greatly enhanced, resulting in improved cycling performance of Li–O₂ batteries. The fundamental stability of the electrolyte in the absence of free‐solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.