Cathode For Lithium-Oxygen Batteries Research Articles

Binder-Free Three-Dimensional Porous Graphene Cathodes via Self-Assembly for High-Capacity Lithium-Oxygen Batteries.

The porous architectures of oxygen cathodes are highly desired for high-capacity lithium-oxygen batteries (LOBs) to support cathodic catalysts and provide accommodation for discharge products. However, controllable porosity is still a challenge for laminated cathodes with cathode materials and binders, since polymer binders usually shield the active sites of catalysts and block the pores of cathodes. In addition, polymer binders such as poly(vinylidene fluoride) (PVDF) are not stable under the nucleophilic attack of intermediate product superoxide radicals in the oxygen electrochemical environment. The parasitic reactions and blocking effect of binders deteriorate and then quickly shut down the operation of LOBs. Herein, the present work proposes a binder-free three-dimensional (3D) porous graphene (PG) cathode for LOBs, which is prepared by the self-assembly and the chemical reduction of GO with triblock copolymer soft templates (Pluronic F127). The interconnected mesoporous architecture of resultant 3D PG cathodes achieved an ultrahigh capacity of 10,300 mAh g-1 for LOBs. Further, the cathodic catalysts ruthenium (Ru) and manganese dioxide (MnO2) were, respectively, loaded onto the inner surface of PG cathodes to lower the polarization and enhance the cycling performance of LOBs. This work provides an effective way to fabricate free-standing 3D porous oxygen cathodes for high-performance LOBs.

Multi-functional integrated design of a copper foam-based cathode for high-performance lithium-oxygen batteries.

Lithium-oxygen batteries (LOBs) with extraordinarily high energy density are some of the most captivating energy storage devices. Designing an efficient catalyst system that can minimize the energy barriers and address the oxidant intermediate and side-product issues is the major challenge regarding LOBs. Herein, we have developed a new type of integrated cathode of Cu foam-supported hierarchical nanowires decorated with highly catalytic Au nanoparticles which achieves a good combination of a gas diffusion electrode and a catalyst electrode, contributing to the synchronous multiphase transport of ions, oxygen, and electrons as well as improving the cathode reaction kinetics effectively. Benefiting from such a unique hierarchical architecture, the integrated cathode delivered superior electrochemical performance, including a high discharge capacity of up to 11.5 mA h cm-2 and a small overpotential of 0.49 V at 0.1 mA cm-2, a favorable energy efficiency of 84.3% and exceptional cycling stability with nearly 1200 h at 0.1 mA cm-2 under a fixed capacity of 0.25 mA h cm-2. Furthermore, density functional theory (DFT) calculations further reveal the intrinsic direct catalytic ability to form/decompose Li2O2 during the ORR/OER process. As a consequence, this work provides an insightful investigation on the structural engineering of catalysts and holds great potential for advanced integrated cathode design for LOBs.

Nitrogen-doped expanded graphite derived from spent graphite induce uniform growth of lithium peroxide for high-performance Li-oxygen battery

Clean treatment and recycling of retired graphite are of great significance to void environmental pollution and resource waste. For this reason, a simple chemical intercalation process combined melamine-assisted expansion strategy is used to prepare nitrogen-doping expanded graphite (N-EG) with a worm-like structure from waste graphite as an ideal lithium-oxygen (Li-O2) battery cathode. The pyrolysis of melamine during annealing can realize the reduction and nitrogen-doping of the expanded graphite in one step, so as to improve the conductivity and electrocatalytic activity of expanded graphite. Moreover, the continuous multilayer hierarchical porous structure of worm-like expanded graphite can not only provide sufficient free-space for the storage of discharge products but also facilitate the mass transfer for battery reactions. As a proof of concept, the as-prepared N-EG have been used as the cathode in Li-O2 battery and achieve excellent electrochemical performances, including high specific capacity, excellent rate performance and long cycle stability. Furthermore, by combining density functional theory (DFT) calculations with experimental data, we demonstrate that the introduction of N-doping in expanded graphite can induce surface combine solution-mediated growth of Li2O2 on the cathode. Such a universal method provides an environmentally friendly approach for the reuse of waste graphite to construct high-performance Li-O2 battery cathode.

Cathode electrocatalyst in aprotic lithium oxygen (Li-O2) battery: A literature survey

Lithium oxygen battery (LOB) is a highly promising energy storage device for the next generation electric vehicles due to its high theoretical energy density. However, many challenges hinder its practical application. The electrochemical performances, such as discharge capacity, discharge and charge overpotentials, power density and stability are all far from satisfactory. In recent years, a great progress has been made and numerous works on cathode materials have been published. This article focuses on the state-of-the-art of LOB cathode materials and the reaction mechanism happens on the cathode. The principles of cathode reactions are summarized and the requirements for cathode materials are discussed. The performance of LOBs with carbon-based and carbon free cathode materials are described. The approaches on improving the cathode performance via temperature increase, material surface engineering, texture optimization and oxygen vacancy regulation are elaborated. A perspective on the research trend on the cathode catalyst is finally proposed.

Carbon nanotube‐supported mixed‐valence Mn3O4 electrodes for high‐performance lithium‐oxygen batteries

Lithium–oxygen batteries (LOBs) have extensive applications because of their ultra-high energy densities. However, the practical application of LOBs is limited by several factors, such as a high overpotential, poor cycle stability, and limited rate capacity. In this paper, we describe the successful uniform loading of Mn3O4 nanoparticles onto multi-walled carbon nanotubes (Mn3O4@CNT). CNTs form a conductive network and expose numerous catalytically active sites, and the one-dimensional porous structure provides a convenient channel for the transmission of Li+ and O2 in LOBs. The electronic conductivity and electrocatalytic activity of Mn3O4@CNT are significantly better than those of MnO@CNT because of the inherent driving force facilitating charge transfer between different valence metal ions. Therefore, the Mn3O4@CNT cathode obtains a low overpotential (0.76 V at a limited capacity of 1000 mAh g−1), high initial discharge capacity (16895 mAh g−1 at 200 mA g−1), and long cycle life (97 cycles at 200 mA g−1). This study provides evidence that transition metal oxides with mixed-valence states are suitable for application as efficient cathodes for LOBs.

High-energy composite cathode for solid-state lithium-oxygen battery boosted by ultrafine carbon nanotube catalysts and amorphous lithium peroxide

Rechargeable solid-state lithium-oxygen batteries (SSLOBs) promise high energy density and safety but suffer from the severe interface impedance in composite cathodes and the failure to detect discharge products by spectroscopy and microscopy originating from low actual discharge capacity. Here, an ultrafine carbon nanotube (CNT) is developed as a cathode catalyst for SSLOBs, which unexpectedly improves the solid-solid contact issue with Li1·5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte and provides a superior specific capacity of 5803 mAh/g (100 mA/g, 2.0–5.0 V vs. Li/Li+) in oxygen atmosphere that is about 4–5 times higher than that of SSLOBs using CNTs with large diameters. This phenomenon is attributed to the optimization of the impedance of CNTs@LAGP induced by the enhanced catalytic activity and enlarged specific surface area of ultrafine CNTs. The amorphous discharge products formed on the CNT surface and between the CNTs and LAGP particles are first found to significantly reduce the cell impedance and increase new reactive sites. Moreover, the irreversible disruption and passivation of CNTs and the accumulation of residual discharge products, which are the fundamental sources of capacity degradation, are further discussed. Importantly, Li2O2 growth morphology as a function of discharge depth and the possible conduction paths of amorphous (Li2O2)n cluster with p-type semiconductor characteristics are also determined by computations based on molecular dynamics and density functional theory for the first time. Our results innovatively reveal the controversial association between impedance and microstructure of composite cathodes, and thus, benefit the development of high-efficiency catalysts and the design of high-energy cathode structures for SSLOBs and other potential solid-state batteries.

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

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

Dual functional mesoporous silica colloidal electrolyte for lithium-oxygen batteries

Dual functional mesoporous silica (mSiO2) colloidal electrolytes are promising to protect lithium anode and accelerate the reaction kinetics on cathode for lithium-oxygen batteries (LOBs).In this work, we achieved a significantly extended battery life (from 55 to 328 cycles) of LOB by using mSiO2 with a concentration of 80 mg L−1 in the colloidal electrolyte, compared with the one using conventional LiClO4/DMSO electrolyte. The rate performance and full-discharge capacity are also dramatically enhanced. The as-synthesized mSiO2 has a special ordered hexagonal mesoporous structure, with a high specific surface area of 1016.30 m2/g, which can form a stable colloid after mixing with 1.0 M LiClO4/DMSO. The side reactions of Li stripping/plating are suppressed, thus the cycling life performance of LOB is enhanced by relieving the attack of superoxide intermediates. The co-deposition of mesoporous mSiO2 and Li2O2 also effectively accelerated the decomposition of the discharge product by promoting the mass transfer at the cathode. This investigation of suppressing side reactions using non-aqueous electrolytes will shed a new light on the design and development of novel lithium metal batteries.

Ultrathin edge-rich structure of Co3O4 enabling the low charging overpotential of Li-O2 battery

• Ultrathin and edge-rich Co 3 O 4 was fabricated and adopted for Li-O 2 catalyst. • The u-Co 3 O 4 tended to induce the formation of thin and loosely aggregated Li 2 O 2 . • High Co 3+ /Co 2+ ratio was benefit for the decomposition of discharge products. The kinetics of the oxygen reduction reaction and oxygen evolution reaction at the rechargeable lithium-oxygen battery cathode are still need to be greatly improved, and transition metal oxides-based catalysts usually suffer from low conductivity and insufficient active sites. Herein, an ultrathin and edge-rich Co 3 O 4 (u-Co 3 O 4 ) catalyst (thickness 3–4 nm) is proposed to lower the overpotential and enhance the cyclability of non-aqueous Li-O 2 battery. The unique structure endows Co 3 O 4 with high electronic conductivity, high specific surface area and abundant active sites. And the high density of Co 3+ ions exposed on surface can serve as active centers for decomposing the discharge products. This u-Co 3 O 4 catalyst tented to induce forming thin and loosely aggregated Li 2 O 2 as discharge products. Electrochemical impedance spectroscopy reveals that a faster charge transmission realized inside the u-Co 3 O 4 -based cell after discharge. Scanning electron microscopy and X-ray diffraction techniques suggest the u-Co 3 O 4 can perfectly catalyze decomposing the discharge products during recharge. Consequently, this u-Co 3 O 4 provided a ∼0.20 V lowered overpotential and an almost 2-fold cycling life for Li-O 2 battery in comparison with traditional Co 3 O 4 catalyst.

Carbon-Free High-Performance Cathode for Solid-State Li–O2 Battery

The development of a cathode for solid-state lithium-oxygen batteries has been hindered in practice by a low capacity and limited cycle life despite their potential for high energy density. Here, a previously unexplored strategy is proposed wherein the cathode delivers a specific capacity of 200 milliampere hour per gram over 665 discharge/charge cycles, while existing cathodes achieve only ~50 milliampere hour per gram and ~100 cycles. A highly conductive mixed ionic-electronic conductors (MIECs) are designed as a carbon-free cathode by first-principles calculations with a density functional theory (DFT) and nudged elastic band (NEB) to avoid the degradation associated with carbonaceous materials, implying an improvement in stability during the electrochemical cycling [1]. In addition, water vapor is added into the main oxygen gas as an additive to change the discharge product from growth-restricted lithium peroxide to easily grown lithium hydroxide, resulting in a significant increase in capacity [2]. Thus, the proposed strategy is effective for developing reversible solid-state lithium-oxygen batteries with high energy density. We will discuss on the systematic materials design and their electrochemical properties for solid-state lithium-oxygen batteries at the meeting.

Compressible, gradient-immersion, regenerable carbon nanotube sponges as high-performance lithium–oxygen battery cathodes

Lithium–oxygen batteries promise ultrahigh energy density, yet one of the key barriers toward applications is the rapid performance decay during cycling especially at high rates, owing to the sluggish redox kinetics and severe parasitic reactions under elevated overpotentials within the cathode. In face of the above challenge, here we present a carbon nanotube sponge-based high-performance lithium–oxygen cathode by a series of approaches such as tailoring discharge product morphology to lower the overpotential, controlled sponge-compression for high mass loading to facilitate high-rate cycling, gradient electrolyte-immersion to rationally utilize its interior for efficient multiphase transport, and water treating for regenerated use. These 4 methods target different aspects of the electrochemical behavior in a Li–O2 cathode, thus constituting a complementary and integrated strategy to overcome the challenges in this field. As a result, we achieve simultaneously an ultralong cycle life (1423 cycles, 2846 h) at high rate (0.5 mA cm−2) under low overpotential (charging below 4.0 V throughout 1100 cycles), also with an areal capacity over 20 mAh cm−2 and extended 500 cycles after regeneration. Such an overall performance is much superior to recently developed 3D metal foam or carbon-based cathodes. Our designed sponge cathode represents a promising candidate for developing durable, high-energy and high-power metal–air battery systems, pushing forward their practical application.

Recent Progress of Catalytic Cathodes for Lithium-oxygen Batteries

Lithium-oxygen batteries are among the most promising electrochemical energy storage systems, which have attracted significant attention in the past few years duo to its far more energy density than lithium-ion batteries. Lithium oxygen battery energy storage is a reactive storage mechanism, and the discharge and charge processes are usually called oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Consequently, complex systems usually create complex problems, lithium oxygen batteries also face many problems, such as excessive accumulation of discharge products (Li2O2) in the cathode pores, resulting in reduced capacity, unstable cycling performance and so on. Cathode catalyst, which could influence the kinetics of OER and ORR in lithium oxygen (Li-O2) battery, is one of the decisive factors to determine the electrochemical performance of the battery, so the design of cathode catalyst is vitally important. This review discusses the catalytic cathode materials, which are divided into four parts, carbon based materials, metals and metal oxides, composite materials and other materials.

Integrated Ni-CNT as a bifunctional catalyst for Li-O2 batteries

Using thermal evaporation technology, Ni-CNT are grown in-situ on nickel plates as the cathode of Li-O2 batteries. This integrated electrode structure eliminates the negative impact of binders on the electrochemical performance and greatly reduces the process for preparing the lithium oxygen battery cathode. Ni-CNT exhibit excellent catalytic activity, and provide an ultrahigh discharge specific capacity of approximately 4.3 mAh cm−2 at 0.1 mA cm−2, the discharge voltage plateau is stable above 2.79 V. In addition, it exhibits a low polarization potential of only 3.34 V during charging, which is much lower than that of the commercial Ru-CNT cathode, and the cycle life of 151 cycles is much higher than that of the commercial Ru-CNT cathode even under a high specific capacity (0.3 mAh cm−2). This self-supporting structure provides abundant space for oxygen transmission and discharge products, and shows great application prospects.

Carbon-free high-performance cathode for solid-state Li-O2 battery.

The development of a cathode for solid-state lithium-oxygen batteries has been hindered in practice by a low capacity and limited cycle life despite their potential for high energy density. Here, a previously unexplored strategy is proposed wherein the cathode delivers a specific capacity of 200 milliampere hour per gram over 665 discharge/charge cycles, while existing cathodes achieve only ~50 milliampere hour per gram and ~100 cycles. A highly conductive ruthenium-based composite is designed as a carbon-free cathode by first-principles calculations to avoid the degradation associated with carbonaceous materials, implying an improvement in stability during the electrochemical cycling. In addition, water vapor is added into the main oxygen gas as an additive to change the discharge product from growth-restricted lithium peroxide to easily grown lithium hydroxide, resulting in a notable increase in capacity. Thus, the proposed strategy is effective for developing reversible solid-state lithium-oxygen batteries with high energy density.

Laser-assisted synthesis of FePc/N-doped carbon dots on Co3O4 flakes as an efficient cathode for lithium-oxygen batteries

Laser-assisted synthesis of FePc/N-doped carbon dots on Co3O4 flakes as an efficient cathode for lithium-oxygen batteries

Highly boron-doped holey graphene for lithium oxygen batteries with enhanced electrochemical performance

The development of advanced catalyst cathode with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities, low cost and rich natural resource is a key to improve the electrochemical performance of rechargeable lithium oxygen batteries (LOBs). Heteroatoms-doped carbon nanomaterials as cathodes for LOBs with improved electrochemical performance have attracted great attentions. Herein, we report an approach to synthesize holey graphene and a boron doped holey graphene (B-hG) with plenty of holey structure and high B doping level of 6 at. %. Benefiting from plenty of holey structures and B related active sites to accelerate the ORR and OER kinetics, the B-hGs (e.g., B-hG-700) cathode displays an extremely high capacity of 19698 mA h g−1 at 100 mA g−1 and long cycling stability over 120 cycles. Both experimental results and density functional theory calculations indicate that the discharge products (e.g., Li2O2) prefer to nucleate and vertically grow near holes/edges sites, which facilitates the formation of relatively isolated and uniformly distributed Li2O2. Such formation process significantly reduces the agglomeration of Li2O2 and effectively provides many spaces to accommodate Li2O2, thus leading to the enhanced ORR and OER kinetic.

MIL-53 Metal-Organic Framework as a Flexible Cathode for Lithium-Oxygen Batteries.

Li-air batteries possess higher specific energies than the current Li-ion batteries. Major drawbacks of the air cathode include the sluggish kinetics of the oxygen reduction (OER), high overpotentials and pore clogging during discharge processes. Metal–Organic Frameworks (MOFs) appear as promising materials because of their high surface areas, tailorable pore sizes and catalytic centers. In this work, we propose to use, for the first time, aluminum terephthalate (well known as MIL-53) as a flexible air cathode for Li-O2 batteries. This compound was synthetized through hydrothermal and microwave-assisted routes, leading to different particle sizes with different aspect ratios. The electrochemical properties of both materials seem to be equivalent. Several behaviors are observed depending on the initial value of the first discharge capacity. When the first discharge capacity is higher, no OER occurs, leading to a fast decrease in the capacity during cycling. The nature and the morphology of the discharge products are investigated using ex situ analysis (XRD, SEM and XPS). For both MIL-53 materials, lithium peroxide Li2O2 is found as the main discharge product. A morphological evolution of the Li2O2 particles occurs upon cycling (stacked thin plates, toroids or pseudo-spheres).

Effect of TiC surface oxide overlayer on the control of LixOy behavior in lithium-oxygen batteries: Implications for cathode catalyst design

TiC has attracted tremendous recent attention in lithium-oxygen batteries as a means of reducing the irreversible accumulation of by-products (i.e., Li2CO3) on the air cathode. However, TiC is intrinsically reactive to oxygen under ambient conditions, and its stability is completely determined by the surface overlayer. Herein, the catalytic effects of oxide overlayer (TiO) on adsorption mechanism, reaction path, and growth morphology of lithium oxides were comprehensively elucidated using periodic density functional theory calculations. The results indicate that the TiO overlayer on the surface of TiC(100)-TiO enhances the adsorption of lithium oxides. As compared to the disproportionation reaction, the lithiation reaction is the primary contributor to the formation of Li2O2 and Li2O on TiC(100) surface. Interestingly, the oxidized TiC(100)-TiO performs better in inhibiting the generation of undesirable Li2O. Analysis demonstrates that the discharge performance is not only related to the widely known morphology and size of product but also to the adsorption of (Li2O2)n clusters on the TiC(100) surface. The electronic structures of (Li2O2)n clusters on TiC(100)-TiC and TiC(100)-TiO surfaces have been examined to study the influence of TiO overlayer on the conductivity of accumulated products, which helps explain the innovative discovery of the experiment that TiC has excellent performance in improving the cycle ability of lithium-oxygen batteries. Our results promote the understanding of the ORR mechanism on TiC surface and provide theoretical guidance for the design of efficient and stable air cathodes for lithium-oxygen batteries.

Highly rechargeable lithium oxygen batteries cathode based on boron and nitrogen co-doped holey graphene

Heteroatoms doped carbon based materials with enhanced catalytic properties hold great potential in energy storage applications, including rechargeable lithium oxygen batteries (LOBs). However, large-scale production of heteroatoms co-doped carbon with high-level dopants as well as the precise control of uniformly distributed dopant location remain challenges. Holey graphene as an emerging carbon based material has attracted increased attention as cathode for LOBs due to its nanoholes through the graphene nanosheet basal plane. Apart from the given rapid diffusion channels for mass (e.g., O2 and Li+ ), the nanoholes also provide rich egdes for the mass adsorption and storage as well as the heteroatoms doping. Herein, we report an environment-friendly and simple approach to mass production of hG with abundant in-plane nanoholes via direct oxidation of reduced graphene oxides (rG) by a controlled flow gas of H2O. Based on the obtained hG, 3.0 at.% B and 2.1 at.% N atoms are further co-doped into the hG to form B, N-hG. Benefiting from its holey structures and the synergistic effect of B and N, the B, N-hG as cathode for LOBs displays promising properties with a maximum discharge capacity of 15340 mAh g−1 and long cycling stability over 117 cycles.

A novel approach to facile synthesis of boron and nitrogen co-doped graphene and its application in lithium oxygen batteries

Rational design of carbon materials for electrochemical devices has attracted great attentions over the past decades. Doping carbon with heteroatoms has been widely proven to be an effective way to improve the physical and electrochemical properties of carbon. The selective types and doping level of heteroatoms, as well as simple and green doping routes, are keys to the development of heteroatoms doped carbon. Due to a strong synergistic effect generated by the co-doping of boron (B) and nitrogen (N), B, N co-doped carbon materials have been demonstrated to be promising catalysts for multiple electrochemical devices. Herein, we report an eco-friendly and one-step approach to synthesis of B, N co-doped graphene (B, N-G) using BN as B and N doping resources. The decomposition of BN under a controlled flow of water steam at high temperature not only enables a high-level B and N co-doping into carbon but also facilitates the formation of highly active catalytic sites. Benefiting from high co-doping level of heteroatoms and highly active catalytic sites (e.g., BC2O), the B, N-G as cathode for rechargeable lithium oxygen batteries displays outstanding lithium storage properties with an ultrahigh specific capacity of 18222 mAh g−1 at 100 mA g−1 and good cycling stability with a limited specific capacity of 1000 mAh g−1 over 120 cycles at 1 A g−1.