Lithium Peroxide Research Articles

Testing a Lithium-Oxygen (Air) Battery: Catalytic Properties of Positive Electrode Materials

Although research in the field of lithium-oxygen (air) batteries (LOB) is rapidly developing, few comprehensive studies on the dependence of the catalytic properties of positive electrode materials on LOB test conditions are present. In this paper, the influence of the current density, the type of oxidizer (pure oxygen or air), and a solvent in the electrolyte (DMSO or tetraglyme) on the electrocatalytic properties of PtM/CNT systems (M = Ru, Co, Cr) used as a positive electrode is investigated. It is shown that at a current density of 500 mA/g, more pronounced catalytic effects are observed during the LOB operation than that at 200 mA/g. The obtained results may be explained by the reduced adverse impact of surface passivation with lithium peroxide in the presence of catalysts compared to a similar effect when using unmodified carbon nanotubes (CNT). It is established that the influence of the current density on the catalytic properties continues upon the transition from oxygen to air as an oxidizer. When studying the effect of electrolytes on the catalytic properties of materials subjected to long-term LOB cycling, it is shown that the catalytic effects are most prominent when charged in a tetraglyme medium. Although using a catalyst has practically no effect on the number of cycles for both electrolytes, LOB having tetraglyme exceeds the cyclability of LOB having DMSO.

In Situ Stress Generation during Oxygen Evolution and Reduction Reactions on Au Positive Electrode in Li-O2 Batteries

Li-O2 batteries have received enormous interest from the scientific community due to its extremely high theoretical specific energy density, which is originated from the oxygen reduction reactions during discharge at the surface of the cathode electrode. Unfortunately, the commercial implementation of this technology is hindered by the poor cycling performance, mostly due to the sluggish oxygen evolution/reduction kinetics and the nature of the discharge reaction product. The lithium peroxide (Li2O2) is the discharge reaction product and its insulating nature limits to harvest the theoretical capacity of the Li-O2 batteries practically. The impact of the salt and solvent species on the formation mechanisms of the discharge product has been reported widely. However, underlying mechanisms dictating the reaction pathway is still under debate.In this study, we employed in situ stress measurement to investigate the impact of the electrolyte salt on nanoscale dynamic changes on the surface of the thin Au film cathode (1-D) during charge / discharge of Li-O2 batteries. Stress measurements have been applied to various electrochemical and electrocatalytic application areas in order to probe the dynamic changes on the surface of the materials. The electrolyte was prepared by mixing 1 M LiTFSI or LiNO3 salts in DMSO or Diglyme solvents. Electrolytes were saturated either with oxygen or argon prior to performing electrochemical measurements. In situ stress measurements were conducted using a multiple beam optical sensor (MOS). A custom cell was designed to monitor the physical response of the cathode during cycling while enabling optical access to the back of the substrate for stress measurements1. In situ curvature evolution on Au thin film cathode was monitored during discharge and charge via galvanostatic cycling and cycling voltammetry.In this talk, we will present the impact of the electrolyte salt on the potential-dependent surface stress generation during the formation and oxidation of electrochemical redox reaction products at nanoscale on the Au thin film cathode. Shortly, in situ stress measurements pointed out the contribution of charge-induced stress, electrostriction stress, and intrinsic stress associated with the formation of discharge reaction products. Revealing the mechanical response of the discharge products on cathode electrode will shed light into the formation mechanisms of these products, which is crucial to design new electrolyte and cathodes for Li-O2 batteries.Acknowledgement:This work was supported by the Binational Science Foundation (#2018327), and we are thankful to both Dr. Malachi Noked and Rosy for fruitful discussions.

Advances in Lithium-Oxygen Batteries Based on Lithium Hydroxide Formation and Decomposition.

The rechargeable lithium-oxygen (Li–O2) batteries have been considered one of the promising energy storage systems owing to their high theoretical energy density. As an alternative to Li−O2 batteries based on lithium peroxide (Li2O2) cathode, cycling Li−O2 batteries via the formation and decomposition of lithium hydroxide (LiOH) has demonstrated great potential for the development of practical Li−O2 batteries. However, the reversibility of LiOH-based cathode chemistry remains unclear at the fundamental level. Here, we review the recent advances made in Li−O2 batteries based on LiOH formation and decomposition, focusing on the reaction mechanisms occurring at the cathode, as well as the stability of Li anode and cathode binder. We also provide our perspectives on future research directions for high-performance, reversible Li−O2 batteries.

Illumination-enhanced oxygen reduction kinetics in hybrid lithium-oxygen battery with p-type semiconductor

Lithium-oxygen battery has attracted extensive attention for its high energy density. However, the lithium peroxide will accumulate at cathode during the discharge process, resulting in large charge–discharge overpotential. At present, the photo-assisted system reported in some work is an effective way to reduce charge overpotential. But the effect of photo-assisted process on the discharge potential is rarely studied. In this work, p-type semiconductor (lanthanum ferrite) was prepared and the photocurrent reaches 179.4 μA cm−2 at 0.7 V (vs RHE) in 0.1 M KOH. It was assembled in the lithium-oxygen battery which was self-designed based on aqueous electrolyte, and the discharge potential of this battery can be improved under illumination due to the enhancement of the oxygen reduction reaction. With light illumination, the LaFeO3 photocathode can promote discharge potential to 3.24 V compare with 2.81 V in dark and stably cycle for more than 400 h.

Cover picture: Investigation into the morphological implications on electron transfer dynamics of lithium peroxides by scanning electrochemical microscopy (BKCS 06/2022)

Elucidation of the morphology‐dependent electron transfer rate was empirically demonstrated by scanning electrochemical microscopy investigation of lithium peroxide species, an important intermediate in the lithium‐air battery cycles. This communication revealed distinct electron transfer coefficients for the toroidal and thin‐film lithium peroxidespecies. This discovery deepens the understanding of battery cycling mechanism and holds the key to unlocking the reversibility of lithium‐air batteries. image

Modeling the multi-step discharge and charge reaction mechanisms of non-aqueous Li-O2 batteries

The modeling study plays a critical role in understanding the reaction mechanisms and predicting the performance of lithium-oxygen (Li-O2) batteries. Although several models have successfully captured the discharge behaviors of the Li-O2 batteries, modeling the charge behaviors of the Li-O2 batteries is a challenge due to lacking a thorough understanding of the related reaction processes. This work proposes a multi-step reversible discharge/charge model for the non-aqueous Li-O2 batteries. Both the surface and solution reaction pathways of lithium peroxide (Li2O2) are taken into account. The proposed model can predict the discharge behaviors well, and more importantly, can accurately capture the charge behaviors of the Li-O2 batteries by considering the following three aspects: the effect of Li2O2 morphology on its decomposition potential, the evolution of interfacial resistance by Li2O2 film collapse, and the different desorption rates of absorbed lithium superoxide (LiO2∗) in different electrolytes. Based on this model, the discharge/charge processes of the Li-O2 batteries using dimethoxyethane(DME), tetraethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO) electrolytes, as well as a redox mediator TEMPO, are simulated and verified. The Li2O2 formation/decomposition through the surface and solution pathways are dominated by the specific surface area of the electrode and the potential, respectively. The Li2O2 generated by the solution pathway is more difficult to be decomposed during charge. The use of redox mediator TEMPO lowers the discharge capacity of the Li-O2 batteries due to the weakened solution reaction, while remarkably reduces the reversible capacity loss. The desorption time constant of LiO2∗ in electrolyte is a critical parameter that determines the degree of the reaction through the solution pathway, thus determining the discharge/charge cycling performance of the Li-O2 batteries with various electrolytes.

N,N-Dimethylethanesulfonamide as an Electrolyte Solvent Stable for the Positive Electrode Reaction of Aprotic Li–O2 Batteries

The realization of secondary lithium–oxygen batteries (Li–O2 batteries, LOBs) with large gravimetric energy density requires the development of an innovative electrolyte with high chemical stability that allows the charge–discharge reaction to proceed with low overvoltage. In this study, we evaluated the potential of an electrolyte solvent, N,N-dimethylethanesulfonamide (DMESA) with a sulfonamide functional group, at a current density of 0.4 mA cm–2 and a capacity of 4 mA h cm–2. The voltage at which CO2 was generated during charging was substantially higher than that of a tetraglyme (G4)-based electrolyte with redox mediators, which is one of the standard electrolytes used for LOBs. Experiments using a 13C-containing positive electrode revealed that CO2 generated during charging mainly originated from the decomposition of the positive electrode. The analyses of the charging profile in conjunction with differential electrochemical mass spectrometry suggested the formation of highly degradable lithium peroxide (Li2O2) in the DMESA-based electrolyte. The formation of highly degradable Li2O2 enables a reduction of the charging voltage, leading to further suppression of the electrolyte decomposition.

Investigation into the morphological implications on electron transfer dynamics of lithium peroxides by scanning electrochemical microscopy

AbstractLithium–air batteries are highlighted as one of promising next generation battery technology with high gravimetric energy density. To date, however, cyclability of lithium–air batteries has been low, insufficient for commercial use. Many recent research accounts focused on understanding the mechanism of the discharge reaction in attempts to improve the cyclability, and revealed that two structurally distinct lithium peroxide species form during discharge, thin films and toroids, among which toroids formation results in beneficial effects in both cyclability and overall discharge capacity. In this work, scanning electrochemical microscopy was applied to investigate electron transfer dynamics of the two lithium peroxide species, from which a much faster surface electron transfer was observed from lithium peroxide toroids compared to that of thin films. The difference is postulated to stem from the difference in the formation mechanism of the two species.

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.

Metal-organic framework-derived ZrO2/NiCo2O4/graphene mesoporous cake-like structure as enhanced bifunctional electrocatalytic cathodes for long life Li-O2 batteries

Metal-organic frameworks (2D MOFs) have great potential to improve the electrochemical performance of Li-O2 batteries with high O2 accessibility, the catalytic activity of the open active metal sites, and large specific surface areas. Herein, we prepared a 3D hierarchical ZrO2@NiCo2O4/GNS (ZNCO) framework as cathode catalysts in Li-O2 batteries that have been developed to synthesize with Zr/Ni to Co molar ratio of 0.1:1:2 by a facile hydrothermal method. The coating of foreign Zr4+ ions into the nickel cobaltite matrix, have superior oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional activity, and allowed the formation of 3D dimensional networks for oxygen diffusion, electrolyte impregnation, and has very ORR/OER low overpotential due to Zr insertion. Moreover, the ZrO2 coated shell increases the electronic conductivity, porosity, specific surface area, and protects the core and interstitial decoration against lithium peroxide passivation (Li2O2). The electrochemical performance of the 3D hierarchical ZrO2@NiCo2O4/GNS nanocomposite delivers a higher discharge capacity of 9034 mAh g–1 at 50 mA g–1 and a superior cycling performance up to 100 cycles with a limited capacity of 1000 mAh g−1 at 100 mA g−1. An ORR/OER mechanism was suggested to illustrate the interesting growth of spherical-like particle and film-like Li2O2 deposits at the different cycles for the ZrO2@NiCo2O4/GNS cathodes. Such MOF-derived; hierarchical porous nanocomposites can lead to high-performance efficient bifunctional electrocatalysts and enables the formation and decomposition of discharge products (Li2O2) during the discharge-charge process.

Towards a Local In situ X‐ray Nano Computed Tomography under Realistic Cycling Conditions for Battery Research

AbstractPerforming high resolution 3D imaging with transmission X‐ray microscopy (TXM) in an in situ battery system is extremely challenging. We show herein a method to conduct an in situ nano‐X ray Computed Tomography (nano‐XCT) experiment assisted by the in‐line phase contrast technique for low Z elements in batteries. A carbon‐based O2‐cathode of Li‐O2 battery was used for this investigation and the time‐resolved 3D volumes were obtained and successfully reconstructed. Our approach is to perform a nano‐XCT by zooming directly into a laser‐shaped area not larger than 50 μm in an in‐house in situ cell. The rotation axis of the tomography of this cell being parallel to the plan of the electrode, a specific method of preparing the electrode by laser is required. This method is essential in this approach, which allows to minimize the dead angles, align the beam and adjust the focus plan. We have demonstrated in situ observation of the difficult light species, lithium peroxide, in a lithium‐oxygen battery. The time‐resolved 3D volumes obtained showed a force pushing the analyzed area out of the field of view. This is due to the thickening of the lithium foil during the electrochemical process. Although X‐ray Computed‐Tomography (XCT) is often considered non‐invasive and beneficial for the development of an in situ experiment for battery research, here we discuss the effect of the focused beam at the nanoscale with a focusing X‐ray beam. The current contribution opens possibilities of characterization of battery materials by local in situ nano‐XCT under realistic cycling conditions.

Redox Mediator with the Function of Intramolecularly Disproportionating Superoxide Intermediate Enabled High‐Performance Li–O2 Batteries

AbstractThe large charge overpotential and poor cycling stability triggered by sluggish Li2O2 oxidation kinetics and severe superoxide‐related side reactions greatly restrict the development and application of lithium–oxygen batteries. Finding out high‐efficiency catalysts that can effectively facilitate a highly reversible formation/decomposition of lithium peroxide is still a crucial challenge in the field of Li–O2 batteries. Herein, a soluble catalyst of 2,2'‐Azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) diammonium salt (ABTS) that can promote highly reversible formation and decomposition of Li2O2 during discharge and charge processes is reported for the first time. During discharge, it can capture and couple two LiO2 intermediates via its sulfonate and ammonium ions, and induce the intramolecular disproportionation reaction to produce Li2O2 through ionic microenvironment, which not only prompts the solution‐phase growth of Li2O2, but also restricts the reactivity of LiO2 intermediate, thus significantly alleviating the electrode surface passivation issue and suppressing the superoxide‐related side reactions. During charge, it can quickly transport electrons between the electrode and Li2O2 by serving as a new kind of redox mediator (RM), thus greatly facilitating the Li2O2 oxidation kinetics. As a result, the Li–O2 batteries that incorporate ABTS exhibit outstanding electrochemical performance, low charge overpotential, high discharge capacity, and high cycling stability.

Critical Void Dimension of Carbon Frameworks to Accommodate Insoluble Products of Lithium-Oxygen Batteries.

High-energy density lithium-oxygen batteries (LOBs) seriously suffer from poor rate capability and cyclability due to the slow oxygen-related electrochemistry and uncontrollable formation of lithium peroxide (Li2O2) as an insoluble discharge product. In this work, we accommodated the discharge product in macro-scale voids of a carbon-framed architecture with meso-dimensional channels on the carbon frame and open holes connecting the neighboring voids. More importantly, we found that a specific dimension of the voids guaranteed high capacity and cycling durability of LOBs. The best LOB performances were achieved by employing the carbon-framed architecture having voids of 0.8 μm size as the cathode of the LOB when compared with the cathodes having voids of 0.3 and 1.4 μm size. The optimized void size of 0.8 μm allowed only a monolithic integrity of lithium peroxide deposit within a void during discharging. The deposit was grown to be a yarn ball-looking sphere exactly fitting the shape and size of the void. The good electric contact allowed the discharge product to be completely decomposed during charging. On the other hand, the void space was not fully utilized due to the mass transfer pathway blockage at the sub-optimized 0.3 μm and the formation of multiple deposit integrities within a void at the sur-optimized 1.4 μm. Consequently, the critical void dimension at 0.8 μm was superior to other dimensions in terms of the void space utilization efficiency and the lithium peroxide decomposition efficiency, disallowing empty space and side reactions during discharging.

Lithium superoxide encapsulated in a benzoquinone anion matrix

Lithium peroxide is the crucial storage material in lithium-air batteries. Understanding the redox properties of this salt is paramount toward improving the performance of this class of batteries. Lithium peroxide, upon exposure to p-benzoquinone (p-C6H4O2) vapor, develops a deep blue color. This blue powder can be formally described as [Li2O2][Formula: see text] [LiO2][Formula: see text] {Li[p-C6H4O2]}0.7, though spectroscopic characterization indicates a more nuanced structural speciation. Infrared, Raman, electron paramagnetic resonance, diffuse-reflectance ultraviolet-visible and X-ray absorption spectroscopy reveal that the lithium salt of the benzoquinone radical anion forms on the surface of the lithium peroxide, indicating the occurrence of electron and lithium ion transfer in the solid state. As a result, obligate lithium superoxide is formed and encapsulated in a shell of Li[p-C6H4O2] with a core of Li2O2 Lithium superoxide has been proposed as a critical intermediate in the charge/discharge cycle of Li-air batteries, but has yet to be isolated, owing to instability. The results reported herein provide a snapshot of lithium peroxide/superoxide chemistry in the solid state with redox mediation.

Tailoring lithium-peroxide reaction kinetics with CuN2C2 single-atom moieties for lithium-oxygen batteries

Single-atom catalysts (SACs) featuring maximized atom utilization are, in no doubt, playing an increasingly significant role in aprotic lithium-oxygen batteries (LOBs). However, rational design and construction of SACs active sites remain enormously challenging due to the superficial understanding of their structure-function relationship. In this contribution, we provide new insight into the link between the catalytic effects of catalysts and the detailed nucleation/delithiation mechanisms of Li2O2 during the oxygen reduction/evolution reaction (ORR/OER). Here, a CuN2C2 SACs electrocatalyst is tailored for LOBs by a confined self-initiated dispersing strategy. The exposed Cu-N2 moieties as the driving force centers can promote the formation of micron-sized flower-shaped lithium peroxide and further accelerate the decomposition kinetics of lithium peroxide via a one-electron transfer way in turn. Under the catalysis of CuN2C2 SACs, the LOB can operate with low discharge/charge polarization and long-term cycle stability. These encouraging results provide guidance to future design and activity promotion of efficient catalysts for LOBs.

Progress and Prospects in Redox Mediators for Highly Reversible Lithium–Oxygen Batteries: A Minireview

Aprotic lithium–oxygen (Li–O2) batteries have received attention as a result of their high theoretical energy density and potentially low material cost. However, their practical applications are limited by side reactions from extremely active singlet oxygen (1O2), lithium superoxide, and insulated lithium peroxide. The use of redox mediators (RMs) has emerged as a strategy to avoid such irreversible reactions. This review summarizes typical RMs on discharging and charging and their corresponding reaction mechanism. Useful non-electroactive additives are also mentioned for inspiration on RMs preparation. Strategies for suppressing shuttle effects and reducing 1O2-induced degradation are further discussed to achieve high reversibility when using RMs. Finally, prospects and conclusions for reversible Li–O2 cells are presented.

Electronic properties of Ir3Li and ultra-nanocrystalline lithium superoxide formation

Current lithium-oxygen (Li-O2) batteries suffer from large charge overpotentials related to electronic resistivity of the insulating lithium peroxide (Li2O2) discharge product. One potential solution to this challenge is the stabilization of the lithium superoxide (LiO2) discharge intermediate, which has much higher electronic conductivity compared to Li2O2. Cathodes based on small iridium (Ir) nanoparticles have been recently used in a Li-O2 battery to successfully stabilize the LiO2 product, however, the LiO2 had a short lifetime. In the previous study, researchers found that the LiO2 was stabilized on Ir3Li surfaces which were formed from Ir nanoparticles during battery operation. Little is known about the electronic properties of Ir3Li and its role in stabilizing LiO2 product formation. This work provides the first study of the electronic properties of Ir3Li, which was thermally synthesized in bulk prior to implementation on the reduced graphene oxide (rGO) cathode of a Li-O2 cell. The bulk Ir3Li was found to have comparable electrical conductivity to Ir metal, possess metal-like magnetic properties, and has an affinity towards O2 adsorption. The LiO2 discharge product formed from the Li-O2 battery discharge was characterized using Raman spectroscopy, titration, along with a comprehensive transmission electron microscopy (TEM) study. This analysis revealed the formation of ultra-nanocrystalline LiO2 particles greater than 200 nm. This result was attributed to the use of large micron sized Ir3Li particles, which could stabilize larger LiO2 particles compared to previous cathodes that utilized Ir nanoparticles that partially converted to Ir3Li during cycling. These results demonstrate that cathode properties can be modified to stabilize the bulk LiO2 discharge product, which can be useful for the further development of LiO2-based Li-O2 batteries.

A freestanding cathode with bimetallic MOF-based composites anchored on N-doped porous carbon nanofibers for lithium-oxygen batteries

Simultaneously achieving both bifunctional catalysts and flexible self-supported electrodes are urgently in demand to satisfy rechargeable lithium-oxygen (Li-O2) batteries, particularly for wearable devices. Herein, we propose a novel strategy embracing electrospinning and hot-pressing to develop Co-based composites embedded in porous nitrogen-rich carbon nanofibers (ZnCo-NC/NCF) as a freestanding cathode for Li-O2 batteries. The fabricated electrode is obtained through pyrolysis of bimetallic (ZnCo) zeolitic imidazolate frameworks/polyacrylonitrile (PAN) nanofibers (BMZIF/PAN). Benefiting from outstanding mechanical strength of electrospun carbon matrix and abundant porosity originated from decomposition of ZIFs as well as fully exposed Co-Nx active sites, the achieved cathode is capable of excellent flexibility, high specific surface area, great conductivity and good catalytic behaviors towards both oxygen reduction/evolution reactions. Consequently, the corresponding Li-O2 batteries exhibit remarkably decreased voltage gap (0.49 V), high specific areal capacity (9.52 mAh cm−2) and long-term cycling capability (around 42 cycles under a curtailing capacity of 0.25 at 0.04 mA cm−2). Besides, the evolution of the morphology and electrochemical impedance spectroscopy at various reaction states are further investigated, which confirms that ZnCo-NC /NCF cathode enables formation and decomposition of lithium peroxide during charge-discharge period.

Inside Cover Picture

The inside cover picture shows that in situ electrochemical atomic force microscopy is performed to clarify the correlation between the decomposition behavior of toroidal lithium peroxide (Li2O2) and the charging rate in a working Li‐O2 battery. In situ observation reveals that a low charge rate promotes the decomposition of toroidal Li2O2 sufficiently, while a larger charge rate accelerates the decomposition occurring at the Li2O2/electrode interface, causing the irreversible capacity degradation. More details are given in the article by Wen et al. on page 2668—2672.image

A novel Pt/MoS2/CNT composite catalyst for the positive electrode of a Li-O2 battery

A Pt/MoS2/CNT composite catalytic system for the positive electrode of a lithium-oxygen battery (LOB) was synthesized by the polyol method. It was established that the modification of MoS2 with platinum leads to an increase in electron density in the conduction band and an increase in electrical conductivity as compared to the characteristics of unmodified MoS2. The introduction of a mesoporous carbon material (carbon nanotubes, CNTs) provides a surface available for lithium peroxide accumulation. In this case, the Pt/MoS2/CNT system exhibits bifunctional catalytic properties, reducing the charge voltage and increasing the discharge capacity of a LOB as compared to the MoS2/CNT catalyst. In addition, the Pt/MoS2/CNT composite demonstrates a higher activity and reversibility in the oxygen reduction reaction than Pt/CNT, probably due to an increased corrosion resistance of MoS2. According to the results of cyclic tests, LOBs with the Pt/MoS2/CNT system can withstand at least 120 consecutive cycles versus 80 cycles for the MoS2/CNT catalyst.