Co3O4 modified Ag/g-C3N4 composite as a bifunctional cathode for lithium-oxygen battery

Rechargeable lithium-oxygen(Li-O2)batteries have appeal to enormous attention because they demonstrate higher energy density than the state-of-the-art Li-ion batteries.Whereas,their practical application is impeded by several challenging problems,such as the low energy round trip efficiencies and the insufficient cycle life,due to the cathode passivation caused by the accumulation of discharge products.Developing efficient catalyst for oxygen reduction and evolution reactions is effective to reduce the overpotentials in Li-O2cells.In our work,we report a Co3O4modified Ag/g-C3N4nanocomposite as a bifunctional cathode catalyst for Li-O2cells.The g-C3N4substrate prevents the accumulation of Ag and Co3O4nanoparticles and the presence of Ag NPs improves the surface area of g-C3N4and electronic conductivity,significantly improving the oxygen reduction/evolution capabilities of Co3O4.Due to a synergetic effect,the Ag/g-C3N4/Co3O4nanocomposite demonstrates a higher catalytic activity than each individual constituent of Co3O4or Ag/g-C3N4for the ORR/OER on as catalysts in Li-O2cells.As a result,the Ag/gC3N4/Co3O4composite shows impressive electrochemical performance in a Li-O2battery,including high discharge capacity,small gap between charge and discharge potential,and high cycling stability.

Long-cycling lithium-oxygen batteries enabled by tailoring Li nucleation and deposition via lithiophilic oxygen vacancy in Vo-TiO_(2)/Ti_(3)C_(2)Tx composite anodes

Uncontrollable Li dendrite growth and infinite volume fluctuation during durative plating and stripping process gravely hinder the application of metallic Li electrode in lithium-oxygen batteries.Herein,oxygen vacancy-rich TiO_(2)(Vo-TiO_(2))nanoparticles(NPs)uniformly dispersing on Ti_(3)C_(2)T_(x)(Vo-TiO_(2)/Ti_(3)C_(2) T_(x))with excellent lithiophilicity feature are presented as effective composite anodes,on which a dense and uniform Li growth behavior is observed.Based on electrochemical studies,mutiphysics simulation and theoretical calculation,it is found that Vo-TiO_(2) coupling with three dimensional(3 D)conductive Ti_(3)C_(2) T_(x) MXene forms highly ordered lithiophilic sites which succeed in guiding Li ions flux and adsorption,thus modulating the uniform Li nucleation and growth.As a result,this composite electrode is capable of preserving Li with high areal capacity of~10 mAh cm^(-2) without the presence of dendrites and large volume expansion.Consequently,the as-prepared Vo-TiO_(2)/Ti_(3)C_(2) T_(x)@Li anode shows outstanding performance including low voltage hysteresis(~19 mV)and superior durability(over 750 h).When assembling with the Vo-TiO_(2)/Ti_(3)C_(2) T_(x)@Li anodes,lithium-oxygen batteries also deliver enhanced cycling stability and improved rate performance.This work demonstrates the effectiveness of oxygen vacancies in guiding Li nucleating and plating behavior at initial stage and brings a promising strategy for promoting the development of advanced Li metal-based batteries.

Strategies to suppress the shuttle effect of redox mediators in lithium-oxygen batteries

Rechargeable lithium-oxygen(Li-O_(2))batteries are the next generation energy storage devices due to their ultrahigh theoretical capacity.Redox mediators(RMs)are widely used as a homogenous electrocatalyst in non-aqueous Li-O_(2)batteries to enhance their discharge capacity and reduce charge overpotential.However,the shuttle effect of RMs in the electrolyte solution usually leads to corrosion of the Li metal anode and uneven Li deposition on the anode surface,resulting in unwanted consumption of electrocatalysts and deterioration of the cells.It is therefore necessary to take some measures to prevent the shuttle effect of RMs and fully utilize the soluble electrocatalysts.Herein,we summarize the strategies to suppress the RM shuttle effect reported in recent years,including electrolyte additives,protective separators and electrode modification.The mechanisms of these strategies are analyzed and their corresponding requirements are discussed.The electrochemical properties of Li-O_(2)batteries with different strategies are summarized and compared.The challenges and perspectives on preventing the shuttle effect of RMs are described for future study.This review provides guidance for achieving shuttle-free redox mediation and for designing Li-O_(2)cells with a long cycle life,high energy efficiency and highly reversible electrochemical reactions.

C_(60) as a metal-free catalyst for lithium-oxygen batteries

Carbon materials have shown significant potential as catalysts for lithium-oxygen batteries(LOBs).However,the intrinsic carbon sites are typically inert,necessitating extensive modifications and resulting in a limited density of active sites.Here we present C_(60) as a metal-free cathode catalyst for LOBs,using density functional theory calculations and experimental verifications.The lithiation reactions on the pristine carbon sites of C_(60) are energetically favorable due to its curvedπ-conjugation over the pentagon-hexagon networks.The kinetic analysis specifically reveals low energy barriers for Li_(2)O_(2) decomposition and Li diffusion on C_(60).Consequently,C_(60) exhibits significantly higher catalytic activity than typical carbon materials such as graphene and carbon nanotubes.Our electrochemical measurements validate the predictions,notably demonstrating that the intrinsic activity of C_(60) is comparable to that of noble metals.

Recent Advances on Ruthenium-based Electrocatalysts for Lithium-oxygen Batteries

Rechargeable lithium-oxygen(Li-O_(2))batteries have attracted wide attention due to their high energy density.However,the sluggish cathode kinetics results in high overvoltage and poor cycling performance.Ruthenium(Ru)-based electrocatalysts have been demonstrated to be promising cathode catalysts to promote oxygen evolution reaction(OER).It facilitates decomposition of lithium peroxide(Li_(2)O_(2))by adjusting Li_(2)O_(2) morphologies,which is due to the strong interaction between Ru-based catalyst and superoxide anion(O_(2)
)intermediate.In this review,the design strategies of Ru-based electrocatalysts are introduced to enhance their OER catalytic kinetics in Li-O_(2) batteries.Different configurations of Ru-based catalysts,including metal particles(Ru metal and alloys),single-atom catalysts,and Ru-loaded compounds with various substrates(carbon materials,metal oxides/sulfides),have been summarized to regulate the electronic structure and the matrix architecture of the Ru-based electrocatalysts.The structure-property relationship of Ru-based catalysts is discussed for a better understanding of the Li_(2)O_(2) decomposition mechanism at the cathode interface.Finally,the challenges of Ru-based electrocatalysts are proposed for the future development of Li-O_(2) batteries.

2H-MoS_(2)Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

Developing excellent cathode catalysts with superior catalytic activities is essential for the practical application of aprotic lithium-oxygen batteries(LOBs).Herein,we successfully synthesized nitrogen-doped hollow mesoporous carbon spheres encapsulated with molybdenum disulfide(MoS_(2))nanosheets as the cathode catalyst for rechargeable LOBs,and the relationship between the battery performance and structural characteristics was intensively researched.We found that the synergistic effect of the nitrogen-doped mesoporous carbon and MoS_(2)nanosheets endows superior electrocatalytic activities to the composite catalyst.On the one hand,the nitrogen-doped mesoporous carbon could enable fast charge transfer and effectively accommodate more discharging products in the composite skeleton.On the other hand,the thin MoS_(2)nanosheets could promote mass transportation to facilitate the revisable formation and decomposition of the Li2O2 during oxygen reduction reaction and oxygen evolution reaction,and the side reactions were also prevented,apparently due to their full coverage on the composite surfaces.As a result,the catalytic cathode loaded with 2H-MoS_(2)-modified nitrogen-doped hollow mesoporous carbon spheres exhibited excellent electrochemical performance in terms of large discharge-/charge-specific capacities with low overpotentials and extended cycling life,and they hold great promise for acting as the cathode catalyst for high-performance LOBs.

A molecular sieve-containing protective separator to suppress the shuttle effect of redox mediators in lithium-oxygen batteries

Lithium-oxygen(Li-O_(2))batteries have a great potential in energy storage and conversion due to their ultra-high theoretical specific energy,but their applications are hindered by sluggish redox reaction kinetics in the charge/discharge processes.Redox mediators(RMs),as soluble catalysts,are widely used to facilitate the electrochemical processes in the Li-O_(2)batteries.A drawback of RMs is the shuttle effect due to their solubility and mobility,which leads to the corrosion of a Li metal anode and the degradation of the electrochemical performance of the batteries.Herein,we synthesize a polymer-based composite protective separator containing molecular sieves.The nanopores with a diameter of 4Åin the zeolite powder(4A zeolite)are able to physically block the migration of 2,2,6,6-tetramethylpiperidinyloxy(TEMPO)molecules with a larger size;therefore,the shuttle effect of TEMPO is restrained.With the assistance of the zeolite molecular sieves,the cycle life of the Li-O_(2)batteries is significantly extended from~20 to 170 cycles at a current density of 250 mA·g^(-1)and a limited capacity of 500 mAh·g^(-1).Our work provides a highly effective approach to suppress the shuttle effects of RMs and boost the electrochemical performance of Li-O_(2)batteries.

第一性原理研究硼掺杂氧化石墨烯对过氧化锂氧化反应的催化机理

锂-氧电池由于高能量密度在后锂离子电池中脱颖而出,而放电产物过氧化锂缓慢的氧化反应降低了电池的循环性能.因此,提高过氧化锂氧化反应动能、降低充电过电位对于实现高能量密度的可逆锂-氧电池具有重要意义.本文通过第一性原理计算,对比研究了氧化石墨烯(GO)和硼掺杂氧化石墨烯(BGO)对过氧化锂小团簇(Li_(2)O_(2))_(2)氧化反应的催化机理.结果表明,从(Li_(2)O_(2))_(2)团簇转移到GO和BGO上的电荷分别为0.59 e和0.96 e,B掺杂提高了电荷转移.4电子反应过程表明,(Li_(2)O_(2))_(2)团簇倾向于Li-O_(2)-Li分解路径,在GO和BGO上反应的速率决定步均是第三步去锂.在平衡电位下,GO和BGO的充电过电位分别是0.76 V和0.23 V,B掺杂大大降低了锂-氧电池充电过电位.机理分析表明B与O对(Li_(2)O_(2))_(2)团簇起到了协同催化的作用.

Reviewing electrochemical stability of ionic liquids-/deep eutectic solvents-based electrolytes in lithium-ion,lithium-metal and post-lithium-ion batteries for green and safe energy

Sustainable energy is the key issue for the environment protection,human activity and economic development.Ionic liquids(ILs)and deep eutectic solvents(DESs)are dogmatically regarded as green and sustainable electrolytes in lithium-ion,lithium-metal(e.g.,lithium-sulphur,lithium-oxygen)and post-lithium-ion(e.g.,sodium-ion,magnesium-ion,and aluminum-ion)batteries.High electrochemical stability of ILs/DESs is one of the prerequisites for green,sustainable and safe energy;while easy electrochemical decomposition of ILs/DESs would be contradictory to the concept of green chemistry by adding the cost,releasing volatile/hazardous by-products and hindering the recyclability.However,(1)are ILs/DESs-based electrolytes really electrochemically stable when they are not used in batteries?(2)are ILs/DESs-based electrolytes really electrochemically stable in real batteries?(3)how to design ILs/DESs-based electrolytes with high electrochemical stability for batteries to achieve sustainability and green development?Up to now,there is no summary on this topic,to the best of our knowledge.Here,we review the effect of chemical structure and non-structural factors on the electrochemical stability of ILs/DESs in simulated conditions.More importantly,electrochemical stability of ILs/DESs in real lithium-ion,lithium-metal and post-lithium-ion batteries is concluded and compared.Finally,the strategies to improve the electrochemical stability of ILs/DESs in lithium-ion,lithium-metal and post-lithium-ion batteries are proposed.This review would provide a guide to design ILs/DESs with high electrochemical stability for lithium-ion,lithium-metal and postlithium-ion batteries to achieve sustainable and green energy.

Enhanced Redox Electrocatalysis in High‑Entropy Perovskite Fluorides by Tailoring d–p Hybridization

High-entropy catalysts featuring exceptional properties are,in no doubt,playing an increasingly significant role in aprotic lithium-oxygen batteries.Despite extensive effort devoted to tracing the origin of their unparalleled performance,the relationships between multiple active sites and reaction intermediates are still obscure.Here,enlightened by theoretical screening,we tailor a high-entropy perovskite fluoride(KCoMnNiMgZnF_(3)-HEC)with various active sites to overcome the limitations of conventional catalysts in redox process.The entropy effect modulates the d-band center and d orbital occupancy of active centers,which optimizes the d–p hybridization between catalytic sites and key intermediates,enabling a moderate adsorption of LiO_(2)and thus reinforcing the reaction kinetics.As a result,the Li–O2 battery with KCoMnNiMgZnF_(3)-HEC catalyst delivers a minimal discharge/charge polarization and long-term cycle stability,preceding majority of traditional catalysts reported.These encouraging results provide inspiring insights into the electron manipulation and d orbital structure optimization for advanced electrocatalyst.

原位表征技术在锂氧气电池中的研究进展

锂氧气电池以其极高的能量密度受到了科研工作者们的广泛关注。然而,锂氧气电池存在金属锂负极稳定性差、充电过电位高等关键难题,使得电池循环寿命短、能量利用效率低,距离大规模应用还有很长一段距离。为了推动锂氧气电池的发展,越来越多的先进原位表征手段用于研究锂氧气电池的机理和优化电池结构。先进的原位表征技术不仅可以用于获取电池的静态信息,同时能准确获取电池在循环过程中的动态电化学行为以及结构演变过程,对于推动锂氧气电池的发展有着重要意义。本文综述了近年来应用于锂氧气电池原位表征手段的相关研究进展,包括原位显微表征技术、原位X射线表征技术、原位质谱表征技术等。通过具体的研究案例,分析了各种原位表征技术的功能,总结了其在锂氧气电池领域里的具体应用场景,揭示了锂氧气电池更深层次的反应机理,并探讨和展望了未来锂氧气电池研究中需要的先进原位表征技术。

锂氧电池Ti_(2)CT_(x)MXene基催化剂的表面调控

为了提高二维材料Ti_(2)CT_(x)MXene的催化活性,通过碱处理和热处理等表面处理技术对MXene进行调控,扩大MXene层间距,减少电化学活性差的-F端基,形成以丰富-O端基构成的t-Ti_(2)CT_(x)材料,并将其用作锂氧电池氧电极催化剂,研究其对电池性能的影响。结果表明:在100 mA/g电流密度下,t-Ti_(2)CT_(x)锂氧电池放电比容量为13150.2 mA·h/g,放电/充电过电位为0.17/0.65 V,均优于未处理的Ti_(2)CT_(x)电池性能。在电流密度为1000 mA/g、限容为500 mA·h/g条件下,t-Ti_(2)CT_(x)电池可稳定循环125次;限容1000 mA·h/g时可循环105次,且循环过程中放电电压均高于2.5 V,由此说明t-Ti_(2)CT_(x)锂氧电池实现了较好的电化学性能。

Organic ionic plastic crystal as electrolyte for lithium-oxygen batteries

Organic ionic plastic crystals (OIPCs) composed of 1-ethyl-1-methyl pyrrolidinium bis(fluorosulfonyl) imide (P12FSI) and lithium bis(fluorosulfonyl)imide (LiFSI) was used as electrolyte for lithium-oxygen batteries. Since P12FSI-LiFSI electrolyte exhibited high ionic conductivity, good chemical stability and wide electrochemical window, the battery showed good rate capability, excellent cycling stability and can be operated stably for 320 cycles under a fixed capacity of 500 mAh/gcarbon. The use of OIPCs electrolyte could provide a new avenue for the development of high-performance Li-O2 batteries.

Nanostructured Ni/Ti3C2Tx MXene hybrid as cathode for lithium-oxygen battery

Ti3C2 belongs to MXenes family,which is a new two-dimensional material and has been applied in many fields.With simple method of hydrothermal and high temperature calcination,nano structured Ni/Ti3C2Tx hybrid was synthesized.The stable layer structure of Ti3C2 MXene providing high surface area as well as excellent electronic conductivity are beneficial for deposition and decomposition of discharge product Li2O2.Furthermore,possessing special catalytic activity,Ni nanoparticles with size of about 20 nm could accelerate Li2O2 breaking down.Taking advantage of two kinds of materials,Ni/Ti3C2Tx hybrid as cathode of Li-O2 battery can achieve a maximal specific capacity of 20,264 mAh/g in 100 mA/g and 10,699 mAh/g in 500 mA/g at the first cycle.This work confirms that the prepared Ni/Ti3C2Tx hybrid exhibiting better cycling stability points out a new guideline to improve the electrochemical performance of lithium-oxygen batteries.

基于第一性原理高价元素Mo稳定层状富锂锰基材料的氧框架机制

采用基于密度泛函理论的第一性原理计算探究了高价元素Mo取代Mn稳定层状富锂锰基材料氧离子框架机制.Mo掺杂将体积变化率从‒2.95%降至‒0.53%,改善了锂化前后的晶格畸变.空位形成能及巴德电荷分析结果表明,7种氧空位形成能均明显提升,且第一配位氧平均巴德电荷从1.13 e升至1.18 e,抑制了不稳定氧析出;锂化前后氧原子巴德电荷改变量从0.51 e降至0.11 e,表明循环前后的体系均具有良好的氧框架稳定性.通过差分电荷密度计算,发现Mo能够在Li去除后提供电荷补偿,而且Mo掺杂后锂离子迁移速率得到了提升,最低势垒从0.55 eV降至0.42 eV.为高价元素掺杂锂离子电池正极材料奠定了坚实的理论依据.

Dual-function redox mediator enhanced lithium-oxygen battery based on polymer electrolyte

The polymer electrolyte based lithium-oxygen battery has showed higher safety than that of organic liquid electrolyte.However,the energy efficiency and cycling stability are still the challenges for the practical application of lithium-oxygen battery.Herein,the 1,4 para benzoquinone has been demonstrated as dual-function redox mediator for promoting both oxygen reduction and oxygen evolution reactions of lithium-oxygen battery with polymer electrolyte,which have been confirmed by the Cyclic Voltammetry and discharge/charge test of battery under O_(2) gas,as well as the theoretical calculations.Furthermore,the composite cathode that in-situ constructed by polymerizing electrolyte precursors with redox me-diator can be beneficial for the electrochemical reactions.Combing composite cathode and lithium ions source,the polymer electrolyte based lithium-oxygen batteries can operate for long lifetime with low charge potentials and good rate performances.Thus,this work has highlighted the promising implementation of lithium-oxygen battery based on polymer electrolyte,in which the dual-function redox mediator are employed for both discharge and recharge processes.

Free-standing nitrogen doped graphene/Co(OH)_(2) composite films with superior catalytic activity for aprotic lithium-oxygen batteries

The recent boom in large-scale energy storage system promotes the development of lithium-oxygen batteries because of their high theo retical energy density.However,their applications are still limited by the sluggish kinetic,insoluble discharge product deposition and the undesired parasitic reaction.Herein,the free-standing nitrogen doped reduced graphene oxide/Co(OH)_(2)(NRGO/Co(OH)_(2)) composite films were prepared by a facile hydrothermal method,The NRGO/Co(OH)_(2) composite films display interconnected three-dimensional conductive network,which can not only promote the diffusion of O2 and the transport of electrolyte ions,but also provide abundant storage space for discharge products.Moreover,the introduction of nitrogen-containing functional groups results in improved conductivity and electron adsorption ability,which can facilitate electron transport and enhance the surface catalytic activity.Combining with excellent catalytic performance,the lithium-oxygen batteries with NRGO/Co(OH)_(2) composite film cathodes deliver low charge overpotential and excellent cycling performance.

Toward high-performance lithium-oxygen batteries with cobalt-based transition metal oxide catalysts:Advanced strategies and mechanical insights

Aprotic lithium-oxygen(Li-O_(2))batteries represent a promising next-generation energy storage system due to their extremely high theoretical specific capacity compared with all known batteries.Their practical realization is impeded,however,by the sluggish kinetics for the most part,resulting in high overpotential and poor cycling performance.Due to the high catalytic activity and favorable stability of Co-based transition metal oxides,they are regarded as the most likely candidate catalysts,facilitating researchers to solve the sluggish kinetics issue.Herein,this review first presents recent advanced design strategies for Co-based transition metal oxides in Li-O_(2)batteries.Then,the fundamental insights related to the catalytic processes of Co-based transition metal oxides in traditional and novel Li-O_(2)electrochemistry systems are summarized.Finally,we conclude with the current limitations and future development directions of Co-based transition metal oxides,which will contribute to the rational design of catalysts and the practical applications of Li-O_(2)batteries.

Bioinspired Fabrication of Strong Self-Standing Egg-Sugarcane Cathodes for Rechargeable Lithium-Oxygen Batteries

Lithium-oxygen(Li-O_(2))batteries have attracted considerable attention due to their high theoretical energy density.However nonrenewable and high-cost electrode materials have limited their progress.Herein,the authors design and fabricate a three-dimensional freestanding bi-biomass egg-sugarcane(Egg-SC)electrode with excellent structure and performance as the cathode for Li-O_(2) batteries.The open,interconnected microchannels derived from the natural SC can provide sufficient pathways for O_(2) gas diffusion.The heteroatom-doped hollow carbon spheres(HD-HCS)obtained via biomass egg supply many of the triphase active sites for the formation and decomposition of the discharge products of Li2O_(2).Benefiting from the unique nature and structure of the cathode,Li-O_(2) batteries show high-rate capacity of 8.07 mAh cm^(-2) and superior cycle stability of 294 cycles at a current density of 0.1 mA cm^(-2).The excellent performance and structure of the bi-biomass cathode possess great application potential in nature-inspired materials design for the cathodes of Li-O_(2) batteries.

基于V2C催化剂的混合电解质锂空气电池催化机理研究

氧还原反应(ORR)和析氧反应(OER)催化活性的提高可以显著提高混合电解质锂空气电池的性能。二维材料V2C(MXenes)具有丰富的组成、高比表面积和强稳定性等特点,受到广泛关注。本工作基于密度泛函理论(DFT)的第一性原理方法,研究了V2C的电子性质、碱性条件下氧气在V2C表面的最佳吸附位点和氧气在V2C表面的氧化还原过程,计算了V2C的自由能和过电势,最后将其与混合电解质锂空气电池常用的MnO2催化剂进行了比较。结果表明,V2C作为混合电解质锂空气电池催化剂时,比常用的MnO2催化剂的过电势更小,说明该催化剂可以提高电极的催化性能,是一种前景良好的ORR和OER双功能催化剂。