Rechargeable Li-O2 Batteries Research Articles

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.

Urchin-like NiO-NiCo2O4 heterostructure microsphere catalysts for enhanced rechargeable non-aqueous Li-O2 batteries.

Urchin-like NiO-NiCo2O4 microspheres with heterostructures were successfully synthesized through a facile hydrothermal method, followed by thermal treatment. The unique structure of NiO-NiCo2O4 with the synergetic effect between NiCo2O4 and NiO, and the heterostructure favour the catalytic activity towards Li-O2 batteries. NiCo2O4 is helpful for boosting both the oxygen reduction reaction and oxygen evolution reaction for the Li-O2 batteries and NiO is likely to promote the decomposition of certain by-products. The special urchin-like morphology facilitates the continuous oxygen flow and accommodates Li2O2. Moreover, benefitting from the heterostructure, NiO-NiCo2O4 microspheres are able to promote the transport of Li ions and electrons to further improve battery performance. Li-O2 batteries utilizing a NiO-NiCo2O4 microsphere electrode show a much higher specific capacity and a lower overpotential than those with a Super P electrode. Moreover, they exhibit an enhanced cycling stability. The electrode can be continuously discharged and charged without obvious terminal voltage variation for 80 cycles, as the discharge capacity is restricted at 600 mA h g-1, suggesting that NiO-NiCo2O4 is a promising catalyst for Li-O2 batteries.

Spinel NiCo2S4 as Excellent Bi-Functional Cathode Catalysts for Rechargeable Li-O2 Batteries

Developing bi-functional catalyst is an effective way to improve the kinetics of oxygen electrochemistry and promote the performance of Li-O2 batteries. In this study, spinel NiCo2S4 with urchin-like and yolk-shell morphologies were successfully synthesized and evaluated as cathode catalysts for rechargeable Li-O2 batteries. The results demonstrate both NiCo2S4 materials are catalytically active toward ORR/OER, but the urchin-like NiCo2S4 performs better with faster kinetics, higher capacity, lower polarization and longer cycle life. Moreover, cycling performance of the Li-O2 batteries with urchin-like NiCo2S4 is evidently better than the reported data in literatures for the batteries with many other transition metal sulfides.

Enhanced cycling performance of rechargeable Li–O2 batteries via LiOH formation and decomposition using high-performance MOF-74@CNTs hybrid catalysts

Li–O2 batteries have received much attention for next-generation energy storage devices due to their high specific energy. However, Li–O2 batteries still face several challenges including low energy efficiency and poor cycle life, which are mainly caused by the low stability of electrolytes and cathodes towards aggressive reduced oxygen species, e.g., O2− intermediate and Li2O2. It has been reported that water can be used as an effective additive in aprotic Li–O2 batteries to increase the discharge capacity and to alleviate parasitic reactions by solvating and trapping the highly aggressive O2− intermediate. In this study, Mn-MOF-74 nanoparticles directly grown on carbon nanotubes (Mn-MOF-74@CNTs) via a facile additive-mediated synthesis are proposed as catalytic cathode materials for Li–O2 batteries to be operated in humid oxygen environment to generate less-reactive discharge product LiOH compared to Li2O2. Due to the formation of LiOH by the nano-architectured Mn-MOF-74@CNTs hybrid catalyst, Mn-MOF-74@CNTs-based oxygen cathode exhibits less side reactions during battery operation and much-enhanced cycling performance in humid oxygen containing 200 ppm moisture than those of conventional carbon cathodes (Ketjenblack and CNTs) in both dry and humid oxygen where Li2O2 was formed as discharge products. Furthermore, a series of controlled experiments and thermodynamic analysis are conducted to investigate the formation mechanism of LiOH. Based on the results, we report that the formation pathway of LiOH is a chemically-catalytic process via a chemical conversion of Li2O2 occurring at Mn2+/Mn3+ metal centers in Mn-MOF-74@CNTs hybrid, instead of an electrocatalytic process via a direct four-electron reduction of oxygen.

Iron phthalocyanine supported on 3D nitrogen-doped graphene aerogel as an electrocatalyst for non-aqueous Li−O2 batteries

Solid electrocatalysts of iron phthalocyanine (FePc) embedded in 3D porous N-doped graphene aerogel (NGA) are designed and applied as cathode catalysts for non-aqueous lithium-oxygen (Li−O2) batteries. Two composites with different axial bonding types between FePc and NGA, including a coordinate covalent bond (FePc/NGA-c) and non-covalent π−π stacking interaction (FePc/NGA-π), are fabricated by reflux and physical mixing methods, respectively. Systematical characterizations confirmed the FePc/NGA-c composite using axial coordination between FePc and NGA substrate via the FeNC bond exhibited more thermal stability and less stack and aggregation of FePc molecules in the composite. Combining the bifunctional catalytic activity of the FePc molecule with oxygen reduction reaction/oxygen evolution reaction (ORR/OER) processes and a flexible porous 3D structure and N-doping in NGA, the electrochemical test demonstrated both FePc anchored on NGA composites display higher activity as bifunctional catalysts for O2 electrodes in Li−O2 batteries. However, the FePc/NGA-c electrode displays better electrochemical performance than the FePc/NGA-π composite due to the axial covalent connection of the FePc catalyst with NGA substrate, leading to higher electrocatalytic activity and exceptional structural durability during cycling for FePc/NGA-c. This work provides new insight into the steric effect of the coordination bond between FePc and NGA on the electrocatalytic activity of O2 electrodes. These results indicate our unique structural design of FePc/NGA-c using solid FePc axially anchored on NGA via covalent bonding is a promising cathode material for high performance of rechargeable LiO2 batteries.

On the Stability of Nitrate Ion in Rechargeable Li-O2 Batteries

A major challenge in realization of Lithium-O2 batteries (LOB), is the instability and reactivity of metallic lithium under the stringent environment of the LOB cell. LiNO3 was proposed as a promising salt for the LOB, due to its catalytic behavior toward OER. However, previous effects are reported to arise from its reaction with metallic lithium. In the present work, we investigated the behavior of LiNO3 in the LOB, under conditions, where, it cannot undergo direct reactions on metallic lithium. Moreover, the stability of NO3− under the electrochemical conditions of LOB, specifically on the cathode side of the cell remained an unvisited territory. We show here that nitrate is unstable on the surface of the carbon scaffold in presence of superoxide ions. We observed the decomposition of nitrate by XPS and electrochemical means and monitored its occurrence in-operando using online electrochemical mass spectroscopy (OEMS). We also illustrate how the reversible nitrate reduction pathway and the regeneration of nitrate are dependent on the presence/absence of metallic lithium in the cell. This work investigates and discusses the importance of chemical/electrochemical stability of the salt used in LOB, and illustrate how this (generally overlooked) aspect is crucial when choosing LOB electrolyte.

Ordered two-dimensional porous Co3O4 nanosheets as electrocatalysts for rechargeable Li-O2 batteries

Lithium-oxygen batteries have attracted considerable interest in the past a few years, because they have higher theoretical specific energy than Li-ion batteries. However, the available energy densities of the Li-O2 batteries are much less than expected. It is particularly urgent to find catalyst with high activity. Herein, a series of Co3O4 with different morphologies (ordered two-dimensional porous nanosheets, flowerlike and cuboidlike) were successfully prepared through facile hydrothermal and calcination methods. Ordered two-dimensional Co3O4 nanosheets show the best cycling stability. Detailed experimental results reveal that the superiority of the unique two-dimensional uniform porous structures is vital for Li-O2 batteries cathode catalysts. Due to the ordered structures with high surface areas and active sites, the catalysts indicate a high specific discharge capacity of about 10,417 mAh/g at a current density of 200 mA/g, and steadily cycle for more than 50 times with a limited capacity of 1,000 mAh/g.

Facile preparation of unique three-dimensional (3D) α-MnO2/MWCNTs macroporous hybrid as the high-performance cathode of rechargeable Li-O2 batteries

Undoubtedly, there remains an urgent prerequisite to achieve significant advances in both the specific capacity and cyclability of Li-O2 batteries for their practical application. In this work, a series of unique three-dimensional (3D) α-MnO2/MWCNTs hybrids are successfully prepared using a facile lyophilization method and investigated as the cathode of Li-O2 batteries. Thereinto, cross-linked α-MnO2/MWCNTs nanocomposites are first synthesized via a modified chemical route. Results demonstrate that MnO2 nanorods in the nanocomposites have a length of 100–400 nm and a diameter ranging from 5 to 10 nm, and more attractively, the as-lyophilized 3D MnO2/MWCNTs hybrids is uniquely constructed with large amounts of interconnected macroporous channels. The Li-O2 battery with the 3D macroporous hybrid cathode that has a mass percentage of 50% of α-MnO2 delivers a high discharge specific capacity of 8,643 mAh·g−1 at 100 mA·g−1, and maintains over 90 cycles before the discharge voltage drops to 2.0 V under a controlled specific capacity of 1,000 mAh·g−1. It is observed that when being recharged, the product of toroidal Li2O2 particles disappears and electrode surfaces are well recovered, thus confirming a good reversibility. The excellent performance of Li-O2 battery with the 3D α-MnO2/MWCNTs macroporous hybrid cathode is ascribed to a synergistic combination between the unique macroporous architecture and highly efficient bi-functional α-MnO2/MWCNTs electrocatalyst.

An Extremely Simple Method for Protecting Lithium Anodes in Li-O2 Batteries.

Rechargeable Li-O2 batteries have aroused much attention for their high energy density as a promising battery technology; however, the performance of the batteries is still unsatisfactory. Lithium anodes, as one of the most important part of Li-O2 batteries, play a vital role in improving the cycle life of the batteries. Now, a very simple method is introduced to produce a protective film on lithium surface via chemical reactions between lithium metals and 1,4-dioxacyclohexane. The film is mainly composed of ethylene oxide monomers and endows Li-O2 batteries with enhanced cycling stability. The film could effectually reduce the morphology changes and suppress the parasitic reactions of lithium anodes. This simple approach provides a new strategy to protect lithium anodes in Li-O2 batteries.

The Rechargeable Aprotic Lithium-oxygen Battery

Interest in the rechargeable Li-O2 battery is driven by its high theoretical specific energy (3500 Whkg-1).1-2 However, a number of challenges face the realization of practical devices.3-10 Overcoming these challenges requires an understanding of the reactions and processes in the cell, especially at the electrodes. Our focus has been on the reaction at the positive electrode: O2 + 2e- + 2Li+ = Li2O2 This simple reaction belies the complexity of the problems during charge and discharge. Li2O2, is an insulating solid, if it grows on the electrode surface it can only do so to a thickness of approx. 6 to 7 nm. The resulting passivation leads to low rates and low capacities.11 If Li2O2 grows from solution, passivation is avoided, leading to high rates and capacities.12 The solvent donor number is an important factor in controlling which pathway, surface film or solution growth, occurs. Low donor number ethers promote surface films while high donor numbers result in solution growth. Unfortunately, high donor number solvents are more susceptible to decomposition by the reactive O2 - nucleophile (the intermediate in the O2/Li2O2 reaction is LiO2).13 We show that using redox mediator molecules to shuttle electrons between the electrode surface and solution, Li2O2 can be formed and decomposed in solution even in low donor number solvent like ethers.14 As a result, rates and capacities of several mA and mAh cm-2 respectively are observed. The impact of the mediators on solvent and electrode stability will be discussed in the context of the mechanism of Li2O2 formation and decomposition. Ultimately, the Li-O2 cell must operate in air. The effect of H2O in the gas stream and hence in the electrolyte solution on the mechanism of O2/Li2O2 and the effect on cell performance are important. The influence of H2O on the O2 reduction mechanism will be considered. REFERENCES [1] D. Aurbach; B.D. McCloskey; L.F. Nazar; P.G. Bruce, Nature Energy 2016, 1, 16128. [2] J.W. Choi; D. Aurbach, Nature Reviews Materials 2016, 1, 16013. [3] N. Mahne; B. Schafzahl; C. Leypold; M. Leypold, et al., Nature Energy 2017, 2, 17036. [4] K.U. Schwenke; M. Metzger; T. Restle; M. Piana, et al., Journal of The Electrochemical Society 2015, 162 (4), A573-A584. [5] D. Grübl; B. Bergner; D. Schröder; J. Janek, et al., The Journal of Physical Chemistry C 2016, 120 (43), 24623-24636. [6] H.-D. Lim; B. Lee; Y. Zheng; J. Hong, et al., Nature Energy 2016, 1 (6), 16066. [7] B.D. McCloskey; D. Addison, ACS Catalysis 2017, 7 (1), 772-778. [8] S. Ganapathy; J.R. Heringa; M.S. Anastasaki; B.D. Adams, et al., The Journal of Physical Chemistry Letters 2016. [9] A.I. Belova; D.G. Kwabi; L.V. Yashina; Y. Shao-Horn, et al., The Journal of Physical Chemistry C 2017, 121 (3), 1569-1577. [10] D. Krishnamurthy; H.A. Hansen; V. Viswanathan, ACS Energy Letters 2016, 1 (1), 162-168. [11] V. Viswanathan; K.S. Thygesen; J.S. Hummelshoj; J.K. Norskov, et al., Journal of Chemical Physics 2011, 135 (21), 214704. [12] L. Johnson; C. Li; Z. Liu; Y. Chen, et al., Nature Chemistry 2014, 6 (12), 1091-1099. [13] A. Khetan; A. Luntz; V. Viswanathan, The Journal of Physical Chemistry Letters 2015, 6 (7), 1254-1259. [14] X. Gao; Y. Chen; L.R. Johnson; Z.P. Jovanov, et al., Nature Energy 2017, 2, 17118.

Cation Segregation of A-Site Deficiency Perovskite La0.85FeO3-δ Nanoparticles toward High-Performance Cathode Catalysts for Rechargeable Li-O2 Battery.

Cation segregation of perovskite oxide is crucial to develop high-performance catalysts. Herein, we achieved the exsolution of α-Fe2O3 from parent La0.85FeO3-δ by a simple heat treatment. Compared to α-Fe2O3 and La0.85FeO3-δ, α-Fe2O3-LaFeO3- x achieved a significant improvement of lithium-oxygen battery performance in terms of discharge specific capacity and cycling stability. The promotion can be attributed to the interaction between α-Fe2O3 and LaFeO3- x. During the cycling test, α-Fe2O3-LaFeO3- x can be stably cycled for 108 cycles at a limited discharge capacity of 500 mAh g-1 at a current density of 100 mA g-1, which is remarkably longer than those of La0.85FeO3-δ (51 cycles), α-Fe2O3 (21 cycles), and mechanical mixing of LaFeO3 and α-Fe2O3 (26 cycles). In general, these results suggest a promising method to develop efficient lithium-oxygen battery catalysts via segregation.

Dandelion-like α-MnO2 hollow spheres with superior catalytic performance for Li-O2 batteries by a facile in situ pyrolysis

To reduce the severe overpotential of oxygen reduction and evolution reaction (ORR and OER) for rechargeable Li-O2 batteries, the dandelion-like α-MnO2 hollow spheres (HS) with high surface area (105.54 m2 g−1) were prepared by a facile in situ pyrolysis of manganese alkoxide for the first time. The ORR diffusion limiting current density and OER current density at 1.0 versus (Ag/AgCl)/V are 6.32 and 45.82 mA cm−2 at 1600 rpm in alkaline solution, respectively, indicating that dandelion-like α-MnO2-HS catalyst exhibits superior bifunctional catalytic activity. The Li-O2 batteries with α-MnO2-HS catalyst can yield high initial discharge specific capacity of 7897.6 mA h g−1 at 100 mA g−1. Moreover, the cycle life of Li-O2 batteries with α-MnO2-HS catalyst is significantly improved and can sustain 108 cycles. These results indicate that as-fabricated hollow sphere structure without adding any hard templates is favorable for superior bifunctional catalytic activity in aqueous and non-aqueous electrolyte.

A high-performance rechargeable Li–O2 battery with quasi-solid-state electrolyte**Project supported by the National Key R&D Program of China (Grant Nos. 2016YFB0100300 and 2016YFB0100100), the National Basic Research Program of China (Grant No. 2014CB932300), the Beijing Municipal Science & Technology Commission, China (Grant No. D171100005517001), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA09010000), and the National

A novel transparent and soft quasi-solid-state electrolyte (QSSE) was proposed and fabricated, which consists of ionic liquid (PYR14TFSI) and nano-fumed silica. The QSSE demonstrates high ionic conductivity of 4.6 × 10−4 S/cm at room temperature and wide electrochemical stability window of over 5 V. The Li–O2 battery using such quasi-solid-state electrolyte exhibits a low charge-discharge overpotential at the first cycle and excellent long-term cyclability over 500 cycles.

Exploring MXenes as Cathodes for Non-Aqueous Lithium-Oxygen Batteries: Design Rules for Selectively Nucleating Li2 O2.

The potential of MXenes, an emerging class of layered materials, is investigated as cathode materials for rechargeable Li-O2 battery chemistry, exploring MXenes from the primary standpoint of the key challenge of rechargeability, which translates to selectivity towards lithium peroxide, the primary discharge product. This study captures the effects of three primary electronic-structure-tuning variables: The termination group and its coverage of the surface as well as the transition metal. The trends are rationalized with regard to the thermodynamic nucleation overpotential, determined through the computed free energy of the adsorbed intermediate LiO*2 . Design rules for identifying MXene cathode materials are developed based on discharge product selectivity and stability against potential decomposition products. Of all investigated MXenes, analysis suggests that Ni4 N3 (OH)2 exhibits the lowest nucleation overpotential and identifies mixed-transition-metal MXenes as a promising exploration direction.

Electrocatalysts of Mn and Ru oxides loaded on MWCNTS with 3D structure and synergistic effect for rechargeable Li-O2 battery

The structure and electrochemical activity of electrocatalysts play a vital role in lithium-oxygen battery. Herein, three-dimensional Mn and Ru oxides loaded on multiwall carbon nanotubes (RuO2-MnO2/MWCNTs) was synthesized via a one-pot hydrothermal approach and served as cathode of rechargeable lithium-oxygen (Li-O2) batteries. SEM and TEM images both illustrated that RuO2 nanoparticles and MnO2 nanoflakes are well dispersed on the surface of MWCNTs and formed a three-dimensional structure, the cyclic voltammetry studies revealed that the RuO2-MnO2/MWCNTs nanocomposite can effectively integrate the oxygen reduction reaction (ORR) activity of MnO2 and oxygen evolution reaction (OER) activity of RuO2. Electrochemical results demonstrated that the RuO2-MnO2/MWCNTs as oxygen cathode of Li–O2 batteries could maintain a reversible capacity of 1000 mAh g−1 within 94 cycles at a rate of 200 mA g−1 and within 120 cycles at a rate as high as 1000 mA g−1. Moreover, the cell with the catalyst RuO2-MnO2/MWCNTs presented much lower voltage polarization (about 0.68 V at a rate of 50 mA g−1) than that measured with MnO2/MWCNTs during charge/discharge processes. Ex-situ SEM were conducted to investigate the morphology and decomposition of Li2O2, which were formed after discharge and decomposed almost after charge process. The excellent electrochemical performance could be contributed to the three-dimensional structure which benefited the diffusion of oxygen and the storage of Li2O2 as well as the synergy effect of MWCNTs as an ideal conductive support for RuO2-MnO2 as co-catalyst in Li-O2 battery.

Atomic layered deposition iron oxide on perovskite LaNiO3 as an efficient and robust bi-functional catalyst for lithium oxygen batteries

The desirable physi-chemical properties of perovskite oxides make them the promising cathode materials of rechargeable Li-O2 batteries. Much attention is devoted to the structure design and the composite incorporation to develop the catalytic activity and durability of perovskite oxides used in the electrode. Herein, we propose an integration of atomic layered deposition iron oxide and perovskite LaNiO3 as a novel catalyst for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Owing to the unique interconnected structure and the synergistic effect of Fe2O3 and LaNiO3, the 6 nm thick Fe2O3/LaNiO3 hybrid catalyst demonstrates the considerable intrinsic activities, which favorably outperforms other the state of the art perovskite catalysts. In addition, the Li-O2 battery employing this tailored catalyst displays a significantly decreased reduced discharge/charge voltage gap of 0.77 V at 50 mA g−1 with good rate capability and considerable cycle stability, indicating the practical feasibility of Fe2O3/LaNiO3 hybrid as a promising oxygen electrode catalyst for Li-O2 batteries. This study highlights a new and feasible scheme to promote the bi-functionally of perovskite catalysts for the development of Li-O2 batteries and other electrochemical devises.

A Binder-Free Carbon-RuO2 Composite Cathode for Rechargeable Li-O2 Batteries

A rechargeable lithium–oxygen (Li–O2) battery is considered as a promising technology for electrochemical energy storage systems, because its theoretical energy density is about ten times higher than those of state-of-the-art Li-ion batteries. The cathode (positive electrode) for Li–O2 batteries is made of carbon and polymeric binders; however, these constituents undergo parasitic decomposition reactions during battery operation, which in turn causes considerable performance degradation. Therefore, the rational design of the cathode is necessary for building robust and high-performance Li–O2 batteries. Here, a binder-free carbon nanotube (CNT) electrode surface-modified by atomic layer deposition (ALD) of dual acting RuO2 as an inhibitor–promoter is proposed for rechargeable Li–O2 batteries. The electrode architecture was designed and fabricated by taking the following features of CNT and ALD into consideration. (i) A free-standing sheet of CNTs can be prepared via a simple filtration procedure without using any binders. (ii) Given that the surface of multi-walled CNTs is very inert, the ALD process yields preferential nucleation–growth of isolated nanoparticles on defect sites rather than producing continuous films on the entire CNT surface. With its proven activity, therefore, RuO2 anchored preferentially to defect sites can play a dual role as an inhibitor (passivating structural defects on CNTs) and a promoter (facilitating electrochemical Li2O2 decomposition). (iii) The ALD process based on sequential, self-limiting reactions allows for the deposition of highly uniform RuO2 nanoparticles within the three-dimensional CNT electrode, which leads to decreased Ru loading while maintaining high catalytic performance. The binder-free RuO2/CNT cathode shows outstanding electrochemical performance as characterized by small voltage gaps (~0.9 V) as well as excellent cyclability without any signs of capacity decay over 80 cycles. The excellent electrochemical performance could be explained by the unique features of the electrode: (i) the absence of polymeric binders with high reactivity with Li2O2 and (ii) the dual function of RuO2 nanoparticles to inhibit carbon decomposition on CNT defects and to promote electrochemical Li2O2 decomposition.

Inverse Spinel Cobalt–Iron Oxide and N-Doped Graphene Composite as an Efficient and Durable Bifuctional Catalyst for Li–O2 Batteries

Rational design of efficient bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are critical for rechargeable Li–O2 batteries. Here, we report inverse spinel Co[Co,Fe]O4/nitrogen-doped graphene (NG) composite used as a promising catalyst for rechargeable Li–O2 batteries. The cells with Co[Co,Fe]O4/NG catalyst exhibit high initial capacity, remarkable cyclability, and good rate capability. Moreover, the overpotential of the Li–O2 batteries is reduced significantly. The improved ORR/OER performances are attributed to the good property of Co[Co,Fe]O4 with an inverse spinel structure toward ORR and the improved electronic conductivity of N-doped graphene. The density functional theory (DFT) calculation shows the rate limitation step for ORR on the inverse spinel surface is the growth of the Li2O2 cluster while the rate limitation step for the OER pathway is the oxidation of Li2O2. The inverse spinel surface in Co[Co,Fe]O4/NG is more active than that of the normal...

Peanut shaped MnCo2O4 winded by multi-walled carbon nanotubes as an efficient cathode catalyst for Li-O2 batteries

Rechargeable Li-O2 batteries have great potential on achieving large-capacity electrochemical energy storage. However, the poor cyclic stability seriously limits its commercial application. In this paper, peanut shaped MnCo2O4 which winding by multi-walled carbon nanotubes (MCO/MWCNTs) were synthesized through a facile solvothermal method. As-prepared MCO/MWCNTs have a unique hierarchical mesoporous of three-level pore sizes and show good ORR and OER electrocatalytic activity. When MCO/MWCNTs served as cathode catalysts in Li-O2 batteries, the batteries exhibited long cycle life of 120 times at 100 mA g−1 with a limited capacity of 500 mAh g−1 and high discharge capacity up to 8849 mAh g−1 with a restrict voltage of 2 V at 100 mA g−1.

Lithiation/Delithiation Synthesis of Few Layer Silicene Nanosheets for Rechargeable Li-O2 Batteries.

Silicene has recently received increasing interest due to its unique properties. However, the synthesis of silicene remains challenging, which limits its wide applications. In this work, a top-down lithiation and delithiation process is developed to prepare few layer silicene-like nanosheets from ball-milled silicon nanopowders. It is found that delithiation solvent plays a critical role in the structure evolution of the final products. The use of isopropyl alcohol renders 2D silicene-like products 30-100 nm in length and ≈2.4 nm in thickness. The electrochemical characterization analysis suggests that the product shows high performance for rechargeable Li-O2 batteries with 73% energy efficiency and high stability. The top-down synthesis strategy proposed in this work not only provides a new solution to the challenging preparation issue of few layer silicene but also demonstrates the feasibility of producing 2D materials from nonlayered starting structures.