High-performance Li-O2 Batteries Research Articles

Two‐Dimensional Transition Metal Chalcogenides for Alkali Metal Ions Storage

On the heels of exacerbating environmental concerns and ever-growing global energy demand, development of high-performance renewable energy-storage and -conversion devices has aroused great interest. The electrode materials, which are the critical components in electrochemical energy storage (EES) devices, largely determine the energy-storage properties, and the development of suitable active electrode materials is crucial to achieve efficient and environmentally friendly EES technologies albeit the challenges. Two-dimensional transition-metal chalcogenides (2D TMDs) are promising electrode materials in alkali metal ion batteries and supercapacitors because of ample interlayer space, large specific surface areas, fast ion-transfer kinetics, and large theoretical capacities achieved through intercalation and conversion reactions. However, they generally suffer from low electronic conductivities as well as substantial volume change and irreversible side reactions during the charge/discharge process, which result in poor cycling stability, poor rate performance, and low round-trip efficiency. In this Review, recent advances of 2D TMDs-based electrode materials for alkali metal-ion energy-storage devices with the focus on lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), high-energy lithium-sulfur (Li-S), and lithium-air (Li-O2 ) batteries are described. The challenges and future directions of 2D TMDs-based electrode materials for high-performance LIBs, SIBs, PIBs, Li-S, and Li-O2 batteries as well as emerging alkali metal-ion capacitors are also discussed.

Phosphorus vacancies enriched Ni2P nanosheets as efficient electrocatalyst for high-performance Li–O2 batteries

Compared with the lithium-ion batteries (LIBs), lithium-oxygen batteries (LOBs) demonstrate ultra-high theoretical energy density (≈3505 W h kg−1), which arouse tremendous research interest worldwide. However, the serious challenges facing LOBs are the sluggish oxygen redox kinetics during the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process, resulting in poor specific capacity and inferior cyclability. Herein, we fabricate phosphorus vacancies enriched Ni2P nanosheets on carbon cloth (denoted as Vp-Ni2P@CC) via a simple NaBH4 reduction strategy as oxygen electrode for high-performance LOBs. Interestingly, the Vp-Ni2P@CC based LOBs exhibit outstanding performance including large specific capacity (10 796 mA h g−1@500 mA g−1) and excellent cyclability (235 cycles@500 mA g−1) compared with LOBs with the Ni2P@CC electrode. It is found that the abundant phosphorus vacancies in the Vp-Ni2P@CC not only act as active sites for oxygen electrode reactions but also enhance the mobility of electron/Li+, simultaneously promoting the improvement of ORR/OER kinetics. Moreover, the restrained electrons around Ni–P bonds are delocalized due to the presence of phosphorus vacancies, which narrow down the band gap in Vp-Ni2P@CC, eventually contributing to high electrical conductivity and excellent electrocatalytic activity. The study provides a new orientation for further developing oxygen electrode catalysts for LOBs.

High Performance Li-O2 Batteries Enabled with Manganese Sulfide as Cathode Catalyst

Transition metal sulfides (TMSs) are attracting great attention as cathode catalysts of Li-O2 batteries. In this article, both γ-MnS and α-MnS are successfully synthesized and their performance is comparatively investigated when employed as cathode catalyst of Li-O2 batteries. It reveals that both MnS materials are capable of catalyzing oxygen reduction reaction as well as oxygen evolution reaction, but α-MnS demonstrates higher activity and better reversibility. The batteries fabricated with α-MnS deliver higher discharge capacity, lower charge voltage, improved high-rate discharge ability and superior cycling performance. These results are discussed and analyzed with help of various physicochemical techniques and compared with the performance of other reported TMSs and a widely studied oxide counterpart (MnO2) of MnS.

In-situ electrochemical functionalization of carbon materials for high-performance Li–O2 batteries

The development of effective synthetic routes is important to manifest proper nature of specific materials. In-situ electrochemical functionalization possesses great advantages over conventional routes, especially facile way and leading to reaching elaborate sites of functional group. Here, we demonstrate the preparation of functionalized carbons by in-situ electrochemical reduction in an argon atmosphere for application in low-cost, environmentally benign, and high-performance oxygen-electrodes for non-aqueous Li–O 2 batteries. A Li–O 2 battery with functionalized carbon shows a high discharge capacity (100 times that of pristine carbon), high power and cycling stability. The outstanding performance is attributed to the high O 2 affinity of the functionalized carbon surface that facilitates the formation of soluble and diffusible superoxide intermediates by the reduction of the remaining O 2 competing with surface growth for Li 2 O 2 formation. Functionalized carbon materials were prepared using a novel method involving insitu reductive pre-treatment of the carbon electrode in a TEGDME/LiTFSI electrolyte. The Li–O 2 cell applying functionalized carbon shows a high discharge capacity, high power and cycling stability.

Integrated 3D foam-like porous Ni3S2 as improved deposition support for high-performance Li–O2 battery

The development of high efficiency air cathode plays important role in regulating the surface electrochemical process to enhance the performance of Li–O2 battery. Herein, we synthesize an integrated porous Ni3S2 on 3D Ni foam substrate through a facile MOF-derived route, the integrated 3D foam-like porous Ni3S2 catalyst can functional as both current collector and catalyst layer. Benefiting from the unique porous structure and the uniform regulate role of the surface electrochemical reaction, the integrated 3D foam-like catalyst cathode delivers nearly 3 times higher discharge capacity and longer cycling performance than that of the pristine Ni foam. More importantly, the morphology of the formed discharge products exhibits lamellar-like structure and has large radial dimension, the Ni3S2 catalyst layer also plays the role of inducing the formation of LiO2 and decreasing the charge overpotential. This study opens a different and facile horizon to fabricate high-efficient air cathode.

Design of house centipede-like MoC–Mo2C nanorods grafted with N-doped carbon nanotubes as bifunctional catalysts for high-performance Li–O2 batteries

Developing effective bifunctional catalysts to promote Li2O2 oxidation and to realize high-performance Li–O2 batteries with long cycle life is a key challenge. Herein, a house centipede-like bifunctional catalyst consisting of a molybdenum carbide nanorod grafted with N-doped carbon nanotubes (denoted as MoC–Mo2C/NCNTs) is developed for enhancing the performance of Li–O2 batteries. This nanocatalyst is successfully fabricated by the post-treatment of MoO3 nanorods coated with a Co-based zeolitic imidazolate framework (ZIF-67). The obtained MoC–Mo2C/NCNT nanorods have a unique structure with a body comprising small MoC–Mo2C nanocrystals and Co@NCNTs extending like legs from it. This structural architecture not only provides numerous catalytic active sites and sufficient space for accommodating Li2O2 but also facilitates electron transport through the catalytically active NCNT conductive pathways. Consequently, the MoC–Mo2C/NCNTs show substantially improved electrocatalytic performance in Li–O2 batteries with a significantly reduced discharge–charge overpotential (0.50 V), high specific discharge capacity (34,862 mA h g−1 at 200 mA g−1), and long cycle stability (up to 162 cycles at current density of 200 mA g−1) and cut-off capacity of 500 mA h g−1. Preliminary results suggest that the MoC–Mo2C/NCNT nanorod is an efficient, stable bifunctional catalyst for Li–O2 batteries.

An Illumination-Assisted Flexible Self-Powered Energy System Based on a Li-O2 Battery.

The flexible Li-O2 battery is suitable to satisfy the requirements of a self-powered energy system, thanks to environmental friendliness, low cost, and high theoretical energy density. Herein, a flexible porous bifunctional electrode with both electrocatalytic and photocatalytic activity was synthesized and introduced as a cathode to assemble a high-performance Li-O2 battery that achieved an overpotential of 0.19 V by charging with the aid of solar energy. As a proof-of-concept application, a flexible Li-O2 battery was constructed and integrated with a solar cell via a scalable encapsulate method to fabricate a flexible self-powered energy system with excellent flexibility and mechanical stability. Moreover, by exploring the evolution of the electrode morphology and discharge products (Li2 O2 ), the charging process of the Li-O2 battery powered by solar energy and solar cell was demonstrated.

Morphology regulation of Li2O2 by flower-like ZnCo2S4 enabling high performance Li-O2 battery

The development of high-efficiency oxygen electrode with well structural and chemical stability is critical to boost the rapid development of lithium-oxygen (Li-O2) batteries. Which are reckoned as a potent contender for next-generation energy storage devices due to their ultra-high theoretical energy density. Here, a flower-like three-dimensional self-standing ZnCo2S4-based electrode without an addition of binders are fabricated and employing as positive electrode for Li-O2 batteries. The bifunctional catalytic activity of flower-like ZnCo2S4 is conducive to improving the hysteresis kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Representative ultrathin petal edge exposes adequate active sites and provides a sufficient contact interface between Li2O2 and positive electrode, which are essential for reducing the charge overpotential during OER. Compared with the control electrodes, the flower-like ZnCo2S4@Ni-based Li-O2 battery shows decreased overpotential (0.78 V) and improved cycle stability (over 500 cycles).

Macroporous carbon nanofiber decorated with platinum nanorods as free-standing cathodes for high-performance Li–O2 batteries

Free-standing and binder-free cathodes composed of macroporous carbon nanofiber (MCNF) were fabricated by electrospinning for use in a Li–O2 battery. The use of cross-linked polystyrene colloids as templates enabled the as-prepared samples to have interconnected macropores along the MCNF interior with numerous surface openings. Additionally, Pt nanorods (PtNRs) were grown as catalysts on the MCNF surface (PtNR-MCNF) to enhance the performance of the Li–O2 battery using the cathode. Owing to the open-pore structure of the cathodes, the Li–O2 cells using the cathodes achieved a specific capacity of approximately 7000 mAh gc−1 and even more at a current density of 200 mA gc−1. In particular, the Li–O2 cell using the PtNR-MCNF cathode exhibited higher electrochemical performance in terms of rate capability, energy efficiency, and cycle stability. This study demonstrates that the growth of PtNRs resulted in the formation of poorly crystalized Li2O2, which significantly reduced the overpotentials, both during the discharge and the charge. Additionally, it contributed to the considerably prolonged cycle life of the Li–O2 cell using the PtNR-MCNF (468 cycles) compared to the cell using the MCNF cathode (272 cycles) with a limiting capacity of 1000 mAh gc−1 at a current density of 500 mA gc−1.

Pt Nanorods-Decorated Macroporous Carbon Nanofiber Free-Standing Cathodes for High-Performance Li-O2 Battery

Controlling the pore structure of cathodes has a strong influence on the performance of Li-O2 battery. In the present study, macroporous carbon nanofiber (MCNF) mats are successfully fabricated through an electrospinning and templating methods using cross-linked polystyrene particles. Additionally, Pt nanorods are grown on the surface of the MCNF (PtNR-MCNF) as catalysts for Li/O2 reactions. As-prepared PtNR-MCNF has interconnected macropores along the MCNF interior and abundant surface openings. Those macropores are also connected to larger pores between individual MCNF through the orifices on the MCNF surface, rendering a hierarchical porous structure. Owing to the highly porous structure, Li-O2 cells using the PtNR-MCNF cathodes achieved a specific capacity of approximately 7,000 mAh/gc and even more at a current density of 200 mA/gc. In particular, the Li-O2 cell using the PtNR-MCNF cathode exhibited higher electrochemical performance in terms of rate capability, energy efficiency, and cycle stability. This study demonstrates that the growth of PtNRs resulted in the formation of poorly crystalized Li2O2, which significantly reduced the overpotentials, both during the discharge and the charge. Additionally, it contributed to the considerably prolonged cycle life of the Li-O2 cell using the PtNR-MCNF (468 cycles) compared to the cell using the MCNF cathode (272 cycles) with a limiting capacity of 1,000 mAh/gc at a current density of 500 mA/gc.

Recent Progress on Catalysts for the Positive Electrode of Aprotic Lithium-Oxygen Batteries †

Rechargeable aprotic lithium-oxygen (Li-O2) batteries have attracted significant interest in recent years owing to their ultrahigh theoretical capacity, low cost, and environmental friendliness. However, the further development of Li-O2 batteries is hindered by some ineluctable issues, such as severe parasitic reactions, low energy efficiency, poor rate capability, short cycling life and potential safety hazards, which mainly stem from the high charging overpotential in the positive electrode side. Thus, it is of great significance to develop high-performance catalysts for the positive electrode in order to address these issues and to boost the commercialization of Li-O2 batteries. In this review, three main categories of catalyst for the positive electrode of Li-O2 batteries, including carbon materials, noble metals and their oxides, and transition metals and their oxides, are systematically summarized and discussed. We not only focus on the electrochemical performance of batteries, but also pay more attention to understanding the catalytic mechanism of these catalysts for the positive electrode. In closing, opportunities for the design of better catalysts for the positive electrode of high-performance Li-O2 batteries are discussed.

Bifunctional perovskite electrocatalyst and PVDF/PET/PVDF separator integrated split test cell for high performance Li-O2 battery

In this work, we have studied the electrochemical performance of split test cell based Li-O2 battery using PVDF/PET/PVDF nanofiber non-woven membrane and La0.5Ce0.5Fe0.5Mn0.5O3 perovskite (denoted as LCFMO) air cathode. The LCFMO air cathode is prepared by a simple wet chemical co-precipitation method and the PVDF/PET/PVDF nanofiber separator is synthesized by an electrospinning method. The as-prepared air cathode and PVDF/PET/PVDF separators are assembled in Li-O2 cell and their charge-discharge profile is evaluated at the potential window of 2–4.5 V at 100 mA g−1 with a limited capacity range of 300, 500 and 1000 mAh g−1. The result certified that the LCFMO-(Urea) catalyst based Li-O2 battery with PVDF/PET/PVDF separator showed an excellent cycling stability over 263, 147 and 120 cycles, respectively. This is due to the excellent bifunctional activity of LCFMO catalyst and high ionic transport properties of PVDF/PET/PVDF membrane. Also, the use of LiI redox mediator can effectively reduce the both charge and discharge overpotential of our Li-O2 battery system. The optimal pore size, higher porosity and good ionic conductivity of the PVDF/PET/PVDF membrane is also an essential factor for the enhanced performance of Li-O2 battery. In addition, AC impedance study evidenced that the Li-O2 battery shows much lower interfacial charge transfer resistance (i.e., lower Rct), which indicates the good electrochemical properties of our proposed materials.

RuO2-particle-decorated graphene-nanoribbon cathodes for long-cycle Li–O2 batteries

In this work, we report a novel cathode composed of three-dimensional intersected graphene nanoribbons skeleton decorated with RuO2 catalyst, where graphene nanoribbons are obtained by unzipping multi-walled carbon nanotubes. The graphene nanoribbons framework exhibits a three-dimensional intersected structure and a large specific surface area, leading to a higher capacity than multi-walled carbon nanotubes. The RuO2 introduced via a facile dropping method enhances the oxygen evolution reaction kinetics and obviously reduces the charge overpotential. More importantly, the Li–O2 battery with RuO2 decorated graphene nanoribbons cathode presents an excellent cycling stability of 424cycles at a curtailed capacity of 1000 mAh g−1, which can be attributed to the synergistic effect between the intersected band-like graphene and highly effective RuO2 particles. The Li2O2 deposited on graphene nanoribbons shows a totally different surface morphology compared with that on multi-walled carbon nanotubes due to the different structures of carbon substrates. This work provides a promising design of highly efficient air electrodes for high-performance Li–O2 batteries.

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.

Biomass-derived hierarchically porous carbon skeletons with in situ decorated IrCo nanoparticles as high-performance cathode catalysts for Li–O2 batteries

Green biomass derived three-dimensional interconnected porous carbon skeletons with in situ decorated IrCo nanoparticles were fabricated for high-performance Li–O2 batteries.

Polysulfide-driven low charge overpotential for aprotic lithium–oxygen batteries

Lithium polysulfide is added to the solvent to realize ultralow charge overpotential for high-performance Li–O2 batteries, where the discharge products of Li2O2 have been replaced with lithium thiosulfate.

Highly reversible Li-O2 battery induced by modulating local electronic structure via synergistic interfacial interaction between ruthenium nanoparticles and hierarchically porous carbon

The interfacial interaction between catalysts and substrates has been considered as a pivotal factor determining the activities in different applications. However, interfacial interaction-dependent catalytic activities are currently neglected in understanding oxygen involved reaction in Li-O2 battery, seriously restricting the development of high performance Li-O2 battery. Herein, Ru@hierarchically porous carbon (Ru@HPC) with well-defined interfaces are fabricated and employed as cathode in Li-O2 battery. Notably, Ru@HPC based Li-O2 battery demonstrate better performance than that based on cathode formed by simply mixing Ru nanoparticles with hierarchically porous carbon (Ru/HPC). The Ru@HPC improved performance with a large specific capacity of ~7100 mA h g−1, high round-trip efficiency of 71%, high rate capability, and excellent cyclic stability of over 125 cycles (over 40 days). Density functional theory calculations indicated that the interfacial interaction between Ru nanoparticles and carbon substrate in Ru@HPC, which triggers electron transfer from ruthenium to carbon and thus optimizes the surface adsorption energy of the reactants and intermediate, facilitates the performance improvement of Li-O2 battery. Our study for the first time reveals that the interfacial interaction between catalyst and substrate is a critical factor determining the Li-O2 battery performance and offers a promising design strategy of catalyst for Li-O2 batteries.

Well-defined carbon nanoframes containing bimetal-N-C active sites as efficient bi-functional electrocatalysts for Li-O2 batteries

Design and fabrication of framework-structured porous precursors have been regarded as a prospective albeit challenging strategy to obtain bimetal/NC-enriched bifunctional elecrocatalysts. In this work, an effective bottom-up approach involving solution-based self-assembly and a post-annealing process was developed to confine (Co, Zn)-N-C active sites into N-enriched graphitic carbon nanocages. This novel architecture containing N-doped-C stabilized bimetallic nanoparticles derived from ZIF precursors was well-studied by a series of characterization and analysis techniques. Details were given that these well-dispersed (Co, Zn) nanoparticles were encapsulated into the pyridinic-N-dominated graphitic carbon nanocage with a total metal loading of approximately 7.4 at.%. This favorable hierarchical structure not only enhances the electron conductivity, but also owns a sufficient BET surface area facilitating the gas-liquid-solid triphase reaction and producing more space to store discharge products. Importantly, results infer that the interesting nanoframes manifests a satisfying ORR/OER activity and enhanced cell performance whether liquid or solid-state electrolytes are used. As such, our work rationalizes that this type of cage-shaped bimetal-N-C material is promising for high-performance Li-O2 batteries.

Three-dimensionally mesoporous dual (Co, Fe) metal oxide/CNTs composite as electrocatalysts for air cathodes in Li-O2 batteries

Developing a stable porous cathode material with efficiently bifunctional activity to ORR/OER is key to achieve the high-performance Li-O2 batteries. Here, a three-dimensional (3D) porous nanoaerogels composed of Co3O4-CoFe2O4/CNTs (CO-CFO/CNTs) nanoparticles is synthesized via a facile alginate-derived biomass conversion strategy combining two-pot calcination method and serves as an effectively bifunctional electrocatalysts for Li-O2 batteries. The as-made electrocatalyst possesses a 3D porous structure with large pore volume, which can effectively shorten diffusion lengths, promote the electron transfer and provide numerous active sites. The CO-CFO/CNTs-based Li-O2 batteries exhibit improved discharge capacity of about 7800.3 mA h g−1 at 100 mA g−1, and achieve a favorable cyclability up to 48 cycles with a fixed capacity of 500 mA h g−1 at 200 mA g−1, due to the co-existence of different functional components of Co3O4 and CoFe2O4 and CNTs conductive network. In addition, the discharge product analysis indicates that the Li2O2 is the dominant product and can be completely decomposed, endowing the CO-CFO/CNTs-based Li-O2 batteries with superior performance.

Synthesis of Cobalt Manganese Oxide-Carbon Nanotubes Composite Microspheres As a Bifunctional Cathode Catalyst for Li-O2 Batteries

Although lithium-ion batteries (LIBs) have been widely used in electronic devices, intercalation limits their energy densities, rendering them incapable of meeting the increasing demand for high energy density. Lithium-oxide (Li-O2) batteries are appealing energy storage and conversion devices owing to their remarkably high energy densities (~3500 Wh kg-1), ~8 times higher than those of current LIBs. However, despite great promise, Li-O2 batteries still suffer from low round-trip efficiency, poor cycle life, and voltage decay. It has been revealed that this limited electrochemical performance is mainly attributed to the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the oxygen electrode. The electrochemical performance of Li-O2 batteries is highly dependent on both the materials and architecture of the oxygen electrode. Transition metal oxide nanomaterials have attracted enormous interest as low-cost alternative catalysts to noble-metal catalysts capable of catalyzing both the ORR and OER. In particular, materials with mixed metal compounds play an important role in electrocatalytic reactions, since mixed valence species enhance electrocatalytic activity. However, the poor electronic conductivity limits the catalytic activity of the mixed-valant transition metal oxide. Therefore, nanostructured materials comprising efficient catalyst nanocrystals and carbon materials with high electrical conductivity, high electrocatalytic activities for the ORR and OER, and a well-designed porous structure to accommodate the reaction products have to be developed. A commercial air electrode should be formed by a simple printing process from slurry containing the cathode powders, organic binder, and solvent. Macroporous cathode powders with uniform composition, several microns in size, spherical morphology, and narrow size distribution should be used to form the uniform air electrode in the commercial process. However, studies on cathode microspheres with optimum morphological characteristics and high electrocatalytic activities for ORRs and OERs for Li–O2 batteries are rare. In this study, Mn-Co-O catalyst was studied as electrocatalyst showing high efficiencies for the ORR and OER for Li-O2 batteries. In addition, the optimum structure of carbon nanotube (CNT) microspheres was designed as efficient support material for catalysts with high electrical conductivity and high accommodation ability for Li2O2 products. Consequently, novel and uniquely structured CNT microspheres decorated with Mn-Co-O nanocrystals with a high electrocatalytic activity were designed and synthesized as cathode material for high performance Li–O2 batteries. Macroporous Mn-Co-O-CNT composite microspheres designed as efficient cathode material for Li-O2 batteries were prepared by one-pot spray pyrolysis. The macroporous structure of CNTs facilitated the wetting of the electrolyte and diffusion of oxygen within the electrode and provided plenty of space to accommodate Li2O2 species formed during the discharge process. The Li-O2 batteries with macroporous Mn-CO-O-CNT composite microspheres showed superior properties as cathode material. The new concept studied in this project can be efficiently applied to the development of highly efficient cathode materials for advanced Li-O2 batteries. Figure 1