Realizing the Embedded Growth of Large Li2O2 Aggregations by Matching Different Metal Oxides for High-Capacity and High-Rate Lithium Oxygen Batteries

Constructed Mott-Schottky Heterostructure Catalyst to Trigger Interface Disturbance and Manipulate Redox Kinetics in Li-O2 Battery

Lithium-oxygen batteries (LOBs) with high energy density are a promising advanced energy storage technology. However, the slow cathodic redox kinetics during cycling causes the discharge products to fail to decompose in time, resulting in large polarization and battery failure in a short time. Therefore, a self-supporting interconnected nanosheet array network NiCo2O4/MnO2 with a Mott-Schottky heterostructure on titanium paper (TP-NCO/MO) is ingeniously designed as an efficient cathode catalyst material for LOBs. This heterostructure can accelerate electron transfer and influence the charge transfer process during adsorption of intermediate by triggering the interface disturbance at the heterogeneous interface, thus accelerating oxygen reduction and oxygen evolution kinetics and regulating product decomposition, which is expected to solve the above problems. The meticulously designed unique structural advantages enable the TP-NCO/MO cathode catalyst to exhibit an astounding ultra-long cycle life of 800 cycles and an extraordinarily low overpotential of 0.73 V. This study utilizes a simple method to cleverly regulate the morphology of the discharge products by constructing a Mott-Schottky heterostructure, providing important reference for the design of efficient catalysts aimed at optimizing the adsorption of reaction intermediates.

Unlock Restricted Capacity via OCe Hybridization for LiOxygen Batteries

The aprotic Li-O₂ battery (LOB) has the highest theoretical energy density of any rechargeable batteries. However, such system is largely restricted by the electrochemically formed lithium peroxide (Li₂ O₂ ) on the cathode surface, leading ultimately to low actual capacities and early cell death. In contrast to the surface-mediated growth of thin film with a thickness <50 nm, a non-crystalline Li₂ O₂ film with a thickness of >400 nm can be formed via an optimal OCe hybridized electronic structure. Specially, oxygen can react with dissolved cerium cations in the electrolyte via a cerium-oxygen reaction to form a high-energy faceted cerium oxide catalyst, which not only generates a great number of non-saturable active sites, but also erects electron transport bridges between the lattice O and adjacent Ce atoms. Such CeO orbital hybridization also forms a direct charge transfer channel from Ce-4f of CeO₂ to O 2 2 - ${\rm{O}}_2^{2 - }$ -π* of Li₂ O₂ , eventually leading to submicron-thick Li₂ O₂ shells via a subsequent lithium-oxygen reaction. Relying on the above merits, this work unlocks the rechargeable capacities of LOB from restricted 1000 to unprecedented 10 000 mAh g^-1 with good cyclabilities and reduced charge-discharge overpotentials.

Highly Sensitive and Selective Gas Sensors Based on NiO/MnO2 @NiO Nanosheets to Detect Allyl Mercaptan Gas Released by Humans under Psychological Stress

NiO nanosheets are synthesized in situ on gas sensor chips using a facile solvothermal method. These NiO nanosheets are then used as gas sensors to analyze allyl mercaptan (AM) gas, an exhaled biomarker of psychological stress. Additionally, MnO₂ nanosheets are synthesized onto the surfaces of the NiO nanosheets to enhance the gas-sensing performance. The gas-sensing response of the NiO nanosheet sensor is higher than that of the MnO₂ @NiO nanosheet sensor. The response value can reach 56.69, when the NiO nanosheet sensor detects 40 ppm AM gas. Interestingly, a faster response time (115 s) is obtained when the MnO₂ @NiO nanosheet sensor is exposed to 40 ppm of AM gas. Moreover, the selectivity toward AM gas is about 17-37 times greater than those toward confounders. The mechanism of gas sensing and the factors contributing to the enhance gas response of the NiO and MnO₂ @NiO nanosheets are discussed. The products of AM gas oxidized by the gas sensor are identified by gas chromatography-mass spectrometry (GC/MS). AM gas detection is an unprecedented application for semiconductor metal oxides. From a broader perspective, the developed sensors represent a new platform for the identification and monitoring of gases released by humans under psychological stress, which is increasing in modern life.

Controllable Synthesis of Ultrathin Defect-Rich LDH Nanoarrays Coupled with MOF-Derived Co-NC Microarrays for Efficient Overall Water Splitting

Water electrolysis has attracted immense research interest, nevertheless the lack of low-cost but efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions greatly hinders its commercial applications. Herein, the controllable synthesis of ultrathin defect-rich layered double hydroxide (LDH) nanoarrays assembled on metal-organic framework (MOF)-derived Co-NC microarrays for boosting overall water splitting is reported. The Co-NC microarrays can not only provide abundant nucleation sites to produce a large number of LDH nuclei for favoring the growth of ultrathin LDHs, but also help to inhibit their tendency to aggregate. Impressively, five types of ultrathin bimetallic LDH nanoarrays can be electrodeposited on the Co-NC microarrays, forming desirable nanoarray-on-macroarray architectures, which show high uniformity with thicknesses from 1.5 to 1.9 nm. As expected, the electrocatalytic performance is significantly enhanced by exploiting the respective advantages of Co-NC microarrays and ultrathin LDH nanoarrays as well as the potential synergies between them. Especially, the optimal Co-NC@Ni₂ Fe-LDH as both cathode and anode can afford the lowest cell voltage of 1.55 V at 10 mA cm^-2 , making it one of the best earth-abundant bifunctional electrocatalysts for water electrolysis. This study provides new insights into the rational design of highly-active and low-cost electrocatalysts and facilitates their promising applications in the fields of energy storage and conversion.

Composite NiCo2 O4 @CeO2 Microsphere as Cathode Catalyst for High-Performance Lithium-Oxygen Battery

The large overpotential and poor cycle stability caused by inactive redox reactions are tough challenges for lithium-oxygen batteries (LOBs). Here, a composite microsphere material comprising NiCo₂ O₄ @CeO₂ is synthesized via a hydrothermal approach followed by an annealing processing, which is acted as a high performance electrocatalyst for LOBs. The unique microstructured catalyst can provide enough catalytic surface to facilitate the barrier-free transport of oxygen as well as lithium ions. In addition, the special microsphere and porous nanoneedles structure can effectively accelerate electrolyte penetration and the reversible formation and decomposition process of Li₂ O₂ , while the introduction of CeO₂ can increase oxygen vacancies and optimize the electronic structure of NiCo₂ O₄ , thereby enhancing the electron transport of the whole electrode. This kind of catalytic cathode material can effectively reduce the overpotential to only 1.07 V with remarkable cycling stability of 400 loops under 500 mA g^-1 . Based on the density functional theory calculations, the origin of the enhanced electrochemical performance of NiCo₂ O₄ @CeO₂ is clarified from the perspective of electronic structure and reaction kinetics. This work demonstrates the high efficiency of NiCo₂ O₄ @CeO₂ as an electrocatalyst and confirms the contribution of the current design concept to the development of LOBs cathode materials.

Recent advances in heterostructured cathodic electrocatalysts for non-aqueous Li-O2 batteries

Developing efficient energy storage and conversion applications is vital to address fossil energy depletion and global warming. Li-O2 batteries are one of the most promising devices because of their ultra-high energy density. To overcome their practical difficulties including low specific capacities, high overpotentials, limited rate capability and poor cycle stability, an intensive search for highly efficient electrocatalysts has been performed. Recently, it has been reported that heterostructured catalysts exhibit significantly enhanced activities toward the oxygen reduction reaction and oxygen evolution reaction, and their excellent performance is not only related to the catalyst materials themselves but also the special hetero-interfaces. Herein, an overview focused on the electrocatalytic functions of heterostructured catalysts for non-aqueous Li-O2 batteries is presented by summarizing recent research progress. Reduction mechanisms of Li-O2 batteries are first introduced, followed by a detailed discussion on the typical performance enhancement mechanisms of the heterostructured catalysts with different phases and heterointerfaces, and the various heterostructured catalysts applied in Li-O2 batteries are also intensively discussed. Finally, the existing problems and development perspectives on the heterostructure applications are presented.

Li2 O2 Formation Electrochemistry and Its Influence on Oxygen Reduction/Evolution Reaction Kinetics in Aprotic Li-O2 Batteries

Aprotic Li-O₂ batteries are regarded as the most promising technology to resolve the energy crisis in the near future because of its high theoretical specific energy. The key electrochemistry of a nonaqueous Li-O₂ battery highly relies on the formation of Li₂ O₂ during discharge and its reversible decomposition during charge. The properties of Li₂ O₂ and its formation mechanisms are of high significance in influencing the battery performance. This review article demonstrates the latest progress in understanding the Li₂ O₂ electrochemistry and the recent advances in regulating the Li₂ O₂ growth pathway. The first part of this review elaborates the Li₂ O₂ formation mechanism and its relationship with the oxygen reduction reaction/oxygen evolution reaction electrochemistry. The following part discusses how the cycling parameters, e.g., current density and discharge depth, influence the Li₂ O₂ morphology. A comprehensive summary of recent strategies in tailoring Li₂ O₂ formation including rational design of cathode structure, certain catalyst, and surface engineering is demonstrated. The influence resulted from the electrolyte, e.g., salt, solvent, and some additives on Li₂ O₂ growth pathway, is finally discussed. Further prospects of the ways in making advanced Li-O₂ batteries by control of favorable Li₂ O₂ formation are highlighted, which are valuable for practical construction of aprotic lithium-oxygen batteries.

Single-Atom Ru Implanted on Co3 O4 Nanosheets as Efficient Dual-Catalyst for Li-CO2 Batteries

Li-CO2 battery has attracted extensive attention and research due to its super high theoretical energy density and its ability to fix greenhouse gas CO2 . However, the slow reaction kinetics during discharge/charge seriously limits its development. Hence, a simple cation exchange strategy is developed to introduce Ru atoms onto a Co3 O4 nanosheet array grown on carbon cloth (SA Ru-Co3 O4 /CC) to prepare a single atom site catalyst (SASC) and successfully used in Li-CO2 battery. Li-CO2 batteries based on SA Ru-Co3 O4 /CC cathode exhibit enhanced electrochemical performances including low overpotential, ultra high capacity, and long cycle life. Density functional theory calculations reveal that single atom Ru as the driving force center can significantly enhance the intrinsic affinity for key intermediates, thus enhancing the reaction kinetics of CO2 reduction reaction in Li-CO2 batteries, and ultimately optimizing the growth pathway of discharge products. In addition, the Bader charge analysis indicates that Ru atoms as electron-deficient centers can enhance the catalytic activity of SA Ru-Co3 O4 /CC cathode for the CO2 evolution reaction. It is believed that this work has important implications for the development of new SASCs and the design of efficient catalyst for Li-CO2 batteries.

MnCo2 S4 -CoS1.097 Heterostructure Nanotubes as High Efficiency Cathode Catalysts for Stable and Long-Life Lithium-Oxygen Batteries Under High Current Conditions

Constructing the heterostructures is considered to be one of the most effective methods to improve the poor electrical conductivity and insufficient electrocatalytic properties of metal sulfide catalysts. In this work, MnCo2 S4 -CoS1.097 nanotubes are successfully prepared via a reflux- hydrothermal process. This novel cathode catalyst delivers high discharge/charge specific capacities of 21 765/21 746 mAh g-1 at 200 mA g-1 and good rate capability. In addition, a favorable cycling stability with a fixed specific capacity of 1000 mAh g-1 at high current density of 1000 mA g-1 (167 cycles) and 2000 mA g-1 (57 cycles) are delivered. It is proposed that fast transmission of ions and electrons accelerated by the built-in electric field, multiple active sites from the heterostructure, and nanotube architecture with large specific surface area are responsible for the superior electrochemical performance. To some extent, the rational design of this heterostructured metal sulfide catalyst provides guidance for the development of the stable and efficient cathode catalysts for Li-O2 batteries that can be employed under high current conditions.

Crystal Phase-Controlled Modulation of Binary Transition Metal Oxides for Highly Reversible Li-O2 Batteries

Reducing charge-discharge overpotential of transition metal oxide catalysts can eventually enhance the cell efficiency and cycle life of Li-O₂ batteries. Here, we propose that crystal phase engineering of transition metal oxides could be an effective way to achieve the above purpose. We establish controllable crystal phase modulation of the binary Mn_xCo_1-xO by adopting a cation regulation strategy. Systematic studies reveal an unprecedented relevancy between charge overpotential and crystal phase of Mn_xCo_1-xO catalysts, whereas a dramatically reduced charge overpotential (0.48 V) via a rational optimization of Mn/Co molar ratio = 8/2 is achieved. Further computational studies indicate that the different morphologies of Li₂O₂ should be related to different electronic conductivity and binding of Li₂O₂ on crystal facets of Mn_xCo_1-xO catalysts, finally leading to different charge overpotential. We anticipate that this specific crystal phase engineering would offer good technical support for developing high-performance transition metal oxide catalysts for advanced Li-O₂ batteries.

Cesium Lead Bromide Perovskite-Based Lithium-Oxygen Batteries

The main challenge for lithium-oxygen (Li-O₂) batteries is their sluggish oxygen evolution reaction (OER) kinetics and high charge overpotentials caused by the poorly conductive discharge products of lithium peroxide (Li₂O₂). In this contribution, the cesium lead bromide perovskite (CsPbBr₃) nanocrystals were first employed as a high-performance cathode for Li-O₂ batteries. The battery with a CsPbBr₃ cathode can exhibit the lowest charge overpotential of 0.5 V and the best cycling performance of 400 cycles among all the reported perovskite-based Li-O₂ cells, which represents a new benchmark. Most importantly, the density functional theory (DFT) calculations further prove that the rate limitation step during OER processes is the decomposition of LiO₂ to form O₂ and Li⁺, and the weak adsorption strength between CsPbBr₃ surfaces and LiO₂ results in a low charge overpotential for the CsPbBr₃-based Li-O₂ battery. This work first demonstrates the good potential of CsPbBr₃ for application in metal-air 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.

Atomically dispersed cobalt catalyst anchored on nitrogen-doped carbon nanosheets for lithium-oxygen batteries

Developing single-site catalysts featuring maximum atom utilization efficiency is urgently desired to improve oxidation-reduction efficiency and cycling capability of lithium-oxygen batteries. Here, we report a green method to synthesize isolated cobalt atoms embedded ultrathin nitrogen-rich carbon as a dual-catalyst for lithium-oxygen batteries. The achieved electrode with maximized exposed atomic active sites is beneficial for tailoring formation/decomposition mechanisms of uniformly distributed nano-sized lithium peroxide during oxygen reduction/evolution reactions due to abundant cobalt-nitrogen coordinate catalytic sites, thus demonstrating greatly enhanced redox kinetics and efficiently ameliorated over-potentials. Critically, theoretical simulations disclose that rich cobalt-nitrogen moieties as the driving force centers can drastically enhance the intrinsic affinity of intermediate species and thus fundamentally tune the evolution mechanism of the size and distribution of final lithium peroxide. In the lithium-oxygen battery, the electrode affords remarkably decreased charge/discharge polarization (0.40 V) and long-term cyclability (260 cycles at 400 mA g-1).

Heterostructured NiS2/ZnIn2S4 Realizing Toroid-like Li2O2 Deposition in Lithium-Oxygen Batteries with Low-Donor-Number Solvents

The aprotic lithium-oxygen (Li-O₂) battery has triggered tremendous efforts for advanced energy storage due to the high energy density. However, realizing toroid-like Li₂O₂ deposition in low-donor-number (DN) solvents is still the intractable obstruction. Herein, a heterostructured NiS₂/ZnIn₂S₄ is elaborately developed and investigated as a promising catalyst to regulate the Li₂O₂ deposition in low-DN solvents. The as-developed NiS₂/ZnIn₂S₄ promotes interfacial electron transfer, regulates the adsorption energy of the reaction intermediates, and accelerates O-O bond cleavage, which are convincingly evidenced experimentally and theoretically. As a result, the toroid-like Li₂O₂ product is achieved in a Li-O₂ battery with low-DN solvents via the solvation-mediated pathway, which demonstrates superb cyclability over 490 cycles and a high output capacity of 3682 mA h g^-1. The interface engineering of heterostructure catalysts offers more possibilities for the realization of toroid-like Li₂O₂ in low-DN solvents, holding great promise in achieving practical applications of Li-O₂ batteries as well as enlightening the material design in catalytic systems.

Inhibition of Discharge Side Reactions by Promoting Solution-Mediated Oxygen Reduction Reaction with Stable Quinone in Li-O2 Batteries

Aprotic lithium-oxygen (Li-O₂) batteries with an ultrahigh theoretical energy density have great potential in rechargeable power supply, while their application still faces several challenges, especially poor cycle stability. To solve the problems, one of the effective strategies is to inhibit the generation of the LiO₂ intermediate produced via a surface-mediated oxygen reduction reaction (ORR) pathway, which is an important species inducing byproduct generation and low cell cyclic stability. Herein, a series of quinones and solid materials serve as the solution-mediated and surface-mediated ORR catalysts, and it was found that the generation of LiO₂ and byproducts from solid catalysts was inhibited by quinones. Among the studied quinones, benzo[1,2-b:4,5-b']dithiophene-4,8-dione, a quinone molecule with the advantage of a highly symmetrical planar and conjugated structure and without α-H, exhibits high redox potential, diffusion coefficient, and electrochemical stability, and consequently the best ORR activities and the capability to inhibit byproduct generation. It indicated that the increase of the solution-mediated ORR pathway plays an important role in restraining the discharging side reaction, substantially improving cell cycle stability and capacity. This study provides the theoretical and experimental basis for better understanding the ORR process of Li-O₂ batteries.

Heterostructured CoO-Co3O4 nanoparticles anchored on nitrogen-doped hollow carbon spheres as cathode catalysts for Li-O2 batteries

Lithium-oxygen batteries have received extensive attention due to their high theoretical energy density and environmental friendliness. Herein, CoO-Co3O4 nanoparticles coated on nitrogen-doped hollow carbon spheres (N-HC@CoO-Co3O4) are prepared by a simple method, and N-HC@CoO-Co3O4 when used as the cathode material for a lithium-oxygen battery shows high catalytic performance. The nitrogen-doped hollow carbon spheres not only ensure an ultra-high specific surface area for the accommodation of the Li2O2 discharge products but also provide more reactive sites. CoO-Co3O4 nanoparticles supported on the surface of the nitrogen-doped hollow carbon spheres can effectively catalyze the formation and decomposition of worm-like Li2O2. The batteries assembled with N-HC@CoO-Co3O4 catalysts exhibit reduced overpotential, improved cycling performance, and high rate capability. Ultra-high discharge capacities of 24 265 mA h g-1 at a current density of 300 mA g-1 and 3622 mA h g-1 at a current density of 1000 mA g-1 are obtained. With a cutoff capacity of 500 mA h g-1, the battery with an N-HC@CoO-Co3O4 electrode can reach more than 112 cycles. This research offers new insights into the design of heterostructured oxide catalysts for Li-O2 batteries.

One-Step Route Synthesized Co2 P/Ru/N-Doped Carbon Nanotube Hybrids as Bifunctional Electrocatalysts for High-Performance Li-O2 Batteries

The large-scale commercial application of lithium-oxygen batteries (LOBs) is overwhelmed by the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) associated with insoluble and insulated Li₂ O₂ . Herein, an elaborate design on a highly catalytic LOBs cathode constructed by N-doped carbon nanotubes (CNT) with in situ encapsulated Co₂ P and Ru nanoparticles is reported. The homogeneously dispersed Co₂ P and Ru catalysts can effectively modulate the formation and decomposition behavior of Li₂ O₂ during discharge/charge processes, ameliorating the electronically insulating property of Li₂ O₂ and constructing a homogenous low-impedance Li₂ O₂ /catalyst interface. Compared with Co/CNT and Ru/CNT electrodes, the Co₂ P/Ru/CNT electrode delivers much higher oxygen reduction triggering onset potential and higher ORR and OER peak current and integral areas, showing greatly improved ORR/OER kinetics due to the synergistic effects of Co₂ P and Ru. Li-O₂ cells based on the Ru/Co₂ P/CNT electrode demonstrate improved ORR/OER overpotential of 0.75 V, excellent rate capability of 12 800 mAh g^-1 at 1 A g^-1 , and superior cycle stability for more than 185 cycles under a restricted capacity of 1000 mAh g^-1 at 100 mA g^-1 . This work paves an exciting avenue for the design and construction of bifunctional catalytic cathodes by coupling metal phosphides with other active components in LOBs.

Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions

The aprotic lithium-oxygen (Li-O₂ ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O₂ battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O₂ battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O₂ batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li₂ O₂ and the mechanisms of Li₂ O₂ oxidation to O₂ on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O₂ batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O₂ batteries in the future.

3D Hollow α-MnO2 Framework as an Efficient Electrocatalyst for Lithium-Oxygen Batteries

Lithium-oxygen (Li-O₂ ) batteries are attracting more attention owing to their superior theoretical energy density compared to conventional Li-ion battery systems. With regards to the catalytically electrochemical reaction on a cathode, the electrocatalyst plays a key role in determining the performance of Li-O₂ batteries. Herein, a new 3D hollow α-MnO₂ framework (3D α-MnO₂ ) with porous wall assembled by hierarchical α-MnO₂ nanowires is prepared by a template-induced hydrothermal reaction and subsequent annealing treatment. Such a distinctive structure provides some essential properties for Li-O₂ batteries including the intrinsic high catalytic activity of α-MnO₂ , more catalytic active sites of hierarchical α-MnO₂ nanowires on 3D framework, continuous hollow network and rich porosity for the storage of discharge product aggregations, and oxygen diffusion. As a consequence, 3D α-MnO₂ achieves a high specific capacity of 8583 mA h g^-1 at a current density of 100 mA g^-1 , a superior rate capacity of 6311 mA h g^-1 at 300 mA g^-1 , and a very good cycling stability of 170 cycles at a current density of 200 mA g^-1 with a fixed capacity of 1000 mA h g^-1 . Importantly, the presented design strategy of 3D hollow framework in this work could be extended to other catalytic cathode design for Li-O₂ 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.

Atomic-Thick TiO2(B) Nanosheets Decorated with Ultrafine Co3O4 Nanocrystals As a Highly Efficient Catalyst for Lithium-Oxygen Battery

Development of highly efficient catalysts based on transition metal oxides (TMOs) is desirable and remains a big challenge for lithium-oxygen (Li-O₂) batteries. In the present work, atomic-thick TiO₂(B) nanosheets decorated with ultrafine Co₃O₄ nanocrystals (Co₃O₄-TiO₂(B)) were synthesized and utilized as cathode catalyst in Li-O₂ batteries by designing a hybrid and inducing oxygen vacancies. The XPS characterization results suggested that the introduction of Co₃O₄ nanocrystals could induce numerous oxygen vacancies in the TiO₂(B) nanosheets through Co doping in the hybrid catalyst. The subsequent electrochemical experiments indicated that the Li-O₂ batteries with the prepared hybrid catalysts showed high specific capacity (11000 mAhg^-1), and good cycling stability (200 cycles at a limited capacity of 1000 mAhg^-1) with low polarization (above 2.7 V for discharge medium voltage and below 4.0 V for charge medium voltage within 80 cycles). Furthermore, a possible working mechanism was proposed for a better understanding of the high performance of Co₃O₄-TiO₂(B) catalysts for the Li-O₂ batteries. This work also provided new insights into designing efficient catalysts through interface engineering between 2D (two-dimensional) TMOs and 0D (zero-dimensional) TMOs for Li-O₂ batteries or other catalysis-related fields.

Stable Voltage Cutoff Cycle Cathode with Tunable and Ordered Porous Structure for Li-O2 Batteries

Ordered porous RuO₂ materials with various pore structure parameters are prepared via a hard-template method and are used as the carbon-free cathodes for Li-O₂ batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO₂ on electrochemical performance are systematically studied. Results indicate that specific surface area and pore size determine the specific capacity and round-trip efficiency of Li-O₂ batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li⁺ and O₂ , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO₂ , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li-O₂ battery based on the RuO₂ cathode with an average pore size of 16 nm (RuO₂ -16) exhibits a high round-trip efficiency of ≈75.6% and an excellent cycling stability of up to 70 cycles at 100 mA g^-1 with a voltage window of 2.5-4.0 V. The superior performance of RuO₂ -16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO₂ can effectively reduce parasitic reactions compared with carbon materials.

MnCo2 O4 /MoO2 Nanosheets Grown on Ni foam as Carbon- and Binder-Free Cathode for Lithium-Oxygen Batteries

Carbon is usually used as cathode material for Li-O₂ batteries. However, the discharge product, such as Li₂ O₂ and LiO₂ , could react with carbon to form an insulating lithium carbonate layer, resulting in cathode passivation and capacity fading. To solve this problem, the development of non-carbon cathodes is highly desirable. Herein, we successfully synthesized MnCo₂ O₄ (MCO) nanoparticles anchored on porous MoO₂ nanosheets that are grown on Ni foam (current collector) (MCO/MoO₂ @Ni), acting as a carbon- and binder-free cathode for Li-O₂ batteries, in an attempt to improve the electrical conductivity, electrocatalytic activity, and durability. This MCO/MoO₂ @Ni electrode delivers excellent cyclability (more than 400 cycles) and rate performance (voltage gap of 0.75 V at 5000 mA g^-1 ). Notably, the battery with this electrode exhibits a high energy efficiency (higher than 85 %). The advanced electrochemical performance of MCO/MoO₂ @Ni can be attributed to its high electrical conductivity, excellent stability, and outstanding electrocatalytic activity. This work offers a new strategy to fabricate high-performance Li-O₂ batteries with non-carbon cathode materials.

Functional and stability orientation synthesis of materials and structures in aprotic Li–O2batteries

This review presents the recent advances made in the functional and stability orientation synthesis of materials/structures for Li–O₂batteries.

Facile and scalable carbon- and binder-free electrode materials for ultra-stable and highly improved Li–O2 batteries

A scalable and ultra-stable carbon- and binder-free Ti@Ru material was synthesized which exhibited potential applications in Li–O₂ batteries.