Aprotic Lithium Oxygen Research Articles

Environmental Impact Analysis of Aprotic Li–O2 Batteries Based on Life Cycle Assessment

Aprotic lithium–oxygen (Li–O₂) batteries are a prominent example of ultrahigh energy density batteries. Although Li–O₂ batteries hold a great potential for large-scale electrochemical energy storage and electric vehicles, their implementation is lagging due to the complex reactions occurring at the cathode. Great effort has been applied to find practical cathodes through the incorporation of different materials acting as catalysts. Here we tap into the quantification of the environmental footprint of seven high-performance Li–O₂ batteries. The batteries were standardized to feed a 60 kWh electric vehicle. Life cycle assessment (LCA) methodology is applied to determine and compare how different batteries and respective components contribute to environmental footprints, categorized in 18 groups. To get a bigger picture, results are compared with the environmental burdens of a reference lithium ion battery, reference sodium ion battery, and the average value of lithium–sulfur batteries. Overall, Li–O₂ batteries present lower environmental burdens in 9 impact categories, with similar impacts in 5 categories in comparison with lithium–sulfur and lithium ion batteries. With an average value of 55.76 kg·CO₂ equiv in Global Warming Potential for the whole Li–O₂ battery, the cathode is the major contributor, with a relative weight of 44.5%. These results provide a road map to enable the practical design of sustainable aprotic Li–O₂ batteries within a circular economy perspective.

Surface plasmon mediates the visible light–responsive lithium–oxygen battery with Au nanoparticles on defective carbon nitride

Aprotic lithium-oxygen (Li-O2) batteries have gained extensive interest in the past decade, but are plagued by slow reaction kinetics and induced large-voltage hysteresis. Herein, we use a plasmonic heterojunction of Au nanoparticle (NP)-decorated C3N4 with nitrogen vacancies (Au/NV-C3N4) as a bifunctional catalyst to promote oxygen cathode reactions of the visible light-responsive Li-O2 battery. The nitrogen vacancies on NV-C3N4 can adsorb and activate O2 molecules, which are subsequently converted to Li2O2 as the discharge product by photogenerated hot electrons from plasmonic Au NPs. While charging, the holes on Au NPs drive the reverse decomposition of Li2O2 with a reduced applied voltage. The discharge voltage of the Li-O2 battery with Au/NV-C3N4 is significantly raised to 3.16 V under illumination, exceeding its equilibrium voltage, and the decreased charge voltage of 3.26 V has good rate capability and cycle stability. This is ascribed to the plasmonic hot electrons on Au NPs pumped from the conduction bands of NV-C3N4 and the prolonged carrier life span of Au/NV-C3N4 This work highlights the vital role of plasmonic enhancement and sheds light on the design of semiconductors for visible light-mediated Li-O2 batteries and beyond.

Interrogating Lithium–Oxygen Battery Reactions and Chemistry with Isotope-Labeling Techniques: A Mini Review

Various advanced characterization technologies have been employed to obtain a mechanistic understanding and then to improve the electrochemical performance of the aprotic lithium–oxygen batteries. ...

Impact of a Gold Nanocolloid Electrolyte on Li2O2 Morphology and Performance of a Lithium-Oxygen Battery.

Aprotic lithium-oxygen batteries currently suffer from poor cyclic stability and low achievable energy density. Herein, gold nanoparticles capped with mercaptosuccinic acid are dispersed in 1.0 M LiClO4/dimethyl sulfoxide (DMSO) as a novel electrolyte for lithium-oxygen batteries. Morphological and electrochemical analyses indicate that film-like amorphous lithium peroxide is formed using the gold nanocolloid electrolyte instead of bulk crystals in battery discharging, which apparently increases the conductivity and accelerates the decomposition kinetics of discharge products in recharging, accompanied by the release of incorporated gold nanoparticles with the decomposition of lithium peroxide into the electrolyte. Experiments and theoretical calculations further demonstrate that the suspended gold nanoparticles in the electrolyte can adsorb some intermediates generated by an oxygen reduction reaction, which effectively alleviates the cleavage of the electrolyte and impedes the corrosion of the lithium anode. As a result, the life span of lithium-oxygen batteries is dramatically increased from 55 to 438 cycles, and the rate performance and full-discharge capacity are also massively enhanced. The battery failure is attributed to the degradation of gold nanocolloid electrolytes, and further studies on improvement of colloid stability during battery cycling are underway.

A review of rechargeable aprotic lithium–oxygen batteries based on theoretical and computational investigations

This review covers the recent advances in theoretical and computational investigations on aprotic Li–O2 batteries.

Highly Efficient Oxygen Evolution Reaction in Rechargeable Lithium-Oxygen Batteries with Triethylphosphate-Based Electrolytes

Aprotic lithium-oxygen (Li–O2) batteries are promising candidates for next-generation energy storage devices, because of their much higher potential energy density than Li-ion batteries. However, the practical application of rechargeable Li–O2 batteries has been limited by poor cycle performance, especially the side reactions that lower the oxygen reaction efficiency at the positive electrode. Ideally, reversible two-electron reaction (with O2/e- = 0.5) should proceed during repeated discharge/charge cycles. However, in practice, various side reactions can occur at the same time. Especially, reactive oxygen species (such as O2 -, LiO2, Li2O2, and singlet O2) tend to decompose the electrolyte (both the solvents and anions) via irreversible chemical reactions that form lithium alkyl carbonates as side products [1,2]. Although various organic solvents have been investigated as electrolytes for Li–O2 batteries, an ideal one has yet to be identified [3,4]. In the present study, we tested new types of triethylphosphate-based electrolytes in Li–O2 batteries to possibly avoid the side reactions by the reactive oxygen species, which could lead to highly efficient oxygen evolution and enhanced life span of the battery. Properties of TEP, such as non-flammability, high oxidative stability, moderate viscosity and high boiling point, are advantageous for use in Li–O2 batteries. Although several investigations have been conducted on TEP-based electrolytes with regard to use in Li–O2 batteries [5-7], to our knowledge, this study is the first demonstration that such electrolytes offer highly efficient oxygen evolution reaction during charging process in the actual batteries.We performed in situ mass spectrometry (MS) analyses to quantitatively evaluate O2 evolution during the charging process. For the Li–O2 cell with TEP-based electrolyte containing 3 M LiNO3, the analysis clearly revealed that the O2 evolution rate was almost 100 % of that of the ideal two-electron reaction (O2/e- = 0.5) during the major part of the charging process. However, there was a sharp decrease in O2 evolution rate at around 0.9 mAh/cm2, accompanied by a sharp increase in the CO2 evolution rate. As a result, the total O2 evolution yield during the charging process was about 90 % that of the ideal two-electron reaction.Next, we focus on clarifying the mechanism of CO2 evolution reaction in the final stage of the charging process. Although in situ MS analysis revealed that the O2 evolution rate was almost 100 % of that of the ideal two-electron reaction during the major part of the charging process, it suffered a sharp drop later, especially when the voltage was higher than 4.0 V. Importantly, the decreased O2 evolution rate coincided with an increased CO2 evolution rate, suggesting the need of suppressing CO2 evolution reaction. In our experiment, the carbon electrode and TEP solvent are both possible carbon sources for the CO2. To further clarify the origin of CO2, in situ MS analysis was performed using an electrode containing 13C. When using this electrode, both 13CO2 and 12CO2 were generated when the voltage was higher than 4.0 V, and the 13C/12C ratio in the evolved CO2 was almost identical to the effective surface area ratio of 13C-powder and 12C-CNT in the electrode. These results clearly revealed that the major part of CO2 came from the carbon electrode, not the TEP solvent. This result suggest that this carbon related side reaction is a crucial issue that must be addressed in order to develop rechargeable Li–O2 batteries with high energy densities and long cycle life.Refereces.[1] McCloskey, B. D. et al. Phys. Chem. Lett. 2011, 2, 1161.[2] Feng, S. et al. Mater. Chem. A 2017, 5, 23987.[3] Adams, B. D. et al. Energy Mater. 2014, 5, 1400867[4] Huang, Z. M. et al. Chem. Int. Ed., 2019, 58, 2345.[5] Bryantsev, V. S. et al. Electrochem. Soc. 2013, 160, A160.[6] Xu,W. et al. Journal of Power Sources, 2012, 215, [7] Reeve, Z. E. et al. Phys. Chem. C, 2015, 119, 26840

Highly Efficient Oxygen Evolution Reaction in Rechargeable Lithium–Oxygen Batteries with Triethylphosphate-Based Electrolytes

Aprotic lithium–oxygen (Li–O2) batteries are promising candidates for next-generation energy storage devices because of their much higher potential energy density than Li-ion batteries. However, th...

Heterostructured NiS2/ZnIn2S4 Realizing Toroid-like Li2O2 Deposition in Lithium–Oxygen Batteries with Low-Donor-Number Solvents

The aprotic lithium-oxygen (Li-O2) battery has triggered tremendous efforts for advanced energy storage due to the high energy density. However, realizing toroid-like Li2O2 deposition in low-donor-number (DN) solvents is still the intractable obstruction. Herein, a heterostructured NiS2/ZnIn2S4 is elaborately developed and investigated as a promising catalyst to regulate the Li2O2 deposition in low-DN solvents. The as-developed NiS2/ZnIn2S4 promotes interfacial electron transfer, regulates the adsorption energy of the reaction intermediates, and accelerates O-O bond cleavage, which are convincingly evidenced experimentally and theoretically. As a result, the toroid-like Li2O2 product is achieved in a Li-O2 battery with low-DN solvents via the solvation-mediated pathway, which demonstrates superb cyclability over 490 cycles and a high output capacity of 3682 mA h g-1. The interface engineering of heterostructure catalysts offers more possibilities for the realization of toroid-like Li2O2 in low-DN solvents, holding great promise in achieving practical applications of Li-O2 batteries as well as enlightening the material design in catalytic systems.

Inhibition of Discharge Side Reactions by Promoting Solution-Mediated Oxygen Reduction Reaction with Stable Quinone in Li-O2 Batteries.

Aprotic lithium-oxygen (Li-O2) batteries with an ultrahigh theoretical energy density have great potential in rechargeable power supply, while their application still faces several challenges, especially poor cycle stability. To solve the problems, one of the effective strategies is to inhibit the generation of the LiO2 intermediate produced via a surface-mediated oxygen reduction reaction (ORR) pathway, which is an important species inducing byproduct generation and low cell cyclic stability. Herein, a series of quinones and solid materials serve as the solution-mediated and surface-mediated ORR catalysts, and it was found that the generation of LiO2 and byproducts from solid catalysts was inhibited by quinones. Among the studied quinones, benzo[1,2-b:4,5-b']dithiophene-4,8-dione, a quinone molecule with the advantage of a highly symmetrical planar and conjugated structure and without α-H, exhibits high redox potential, diffusion coefficient, and electrochemical stability, and consequently the best ORR activities and the capability to inhibit byproduct generation. It indicated that the increase of the solution-mediated ORR pathway plays an important role in restraining the discharging side reaction, substantially improving cell cycle stability and capacity. This study provides the theoretical and experimental basis for better understanding the ORR process of Li-O2 batteries.

Potassium Doping Facilitated Formation of Tunable Superoxides in Li2O2 for Improved Electrochemical Kinetics.

Superoxide (O2-) species play a crucial role in determining the charge kinetics for aprotic lithium-oxygen (Li-O2) batteries. However, the growth of O2--rich lithium peroxide (Li2O2) is challenging since O2- is thermodynamically unfavorable and unstable in an O2 atmosphere. Herein, we reported the synthesis of defective Li2O2 with tunable O2- via K+ doping. The K+ dopants can successfully stabilize O2- species and induce the coordination of Li+ with O2-, leading to increased Li vacancies. Compared to the pristine Li2O2, the as-prepared defective Li2O2 can be charged at a lower overpotential in Li-O2 batteries, which is ascribed to further increased Li vacancies contributed by the depotassiation process at the onset of the charge process. Our findings suggest a new strategy to better control O2- species in Li2O2 by K+ dopants and provide insights into the K+ effects on charge mechanism in Li-O2 batteries.

Combinational Design of Electronic Structure and Nanoarray Architecture Achieves a Low‐Overpotential Oxygen Electrode for Aprotic Lithium–Oxygen Batteries

AbstractTransition metal nitrides (TMNs) are generally recognized as excellent electrocatalysts in aqueous solution because of their distinct electronic structures and high electrical conductivity. However, their potential catalytic activities are rarely studied in the oxygen electrodes of aprotic lithium–oxygen batteries and the intrinsic electroactivities are quite difficult to be manifested in binder‐involved electrodes. Herein, a novel combinational design of electronic structure and nanoarray architecture is proposed to eliminate the influences of binders and additives and achieve high performance of TMNs as oxygen electrodes for aprotic lithium–oxygen batteries. In the case study of CoN nanowire arrays (NAs), experimental coupled with theoretical studies demonstrate that the distinct electronic structure of CoN enables the appropriate adsorption and facile charge transfer between the discharge product Li2O2 and CoN. Results also show that the nanoarray architecture of CoN enables the full utilization of catalytic active sites, efficient mass transportation, and sufficient inner spaces for accommodating the insoluble discharge product. Thus, the CoN NA cathode achieves both a low overall overpotential of 1.01 V and a high areal capacity of 3.35 mA h cm−2. The combinational design principle of electronic structure and electrode architecture provides a promising way to develop advanced oxygen electrode for metal–air batteries.

Surface carboxyl groups enhance the capacities of carbonaceous oxygen electrodes for aprotic lithium−oxygen batteries: A direct observation on binder-free electrodes

In order to achieve the high capacities of carbonaceous oxygen diffusion electrodes for aprotic lithium–oxygen batteries (Li–O2 batteries), most efforts currently focus on the design of rational porous architectures. Only few works study the surface chemistry effect that might be a critical factor influencing the capacities of carbonaceous electrodes. In addition, the surface chemistry effect is very difficult to be studied in composite electrodes due to the influences of binders and additives. Herein, we propose chemically activated carbon cloth (CACC) as an ideal model to investigate the effect of surface functional groups on the discharge capacities of carbonaceous oxygen electrodes for Li–O2 batteries. The intrinsic surface chemistry effect on the performance of carbonaceous cathode is directly observed for the first time without the influences of binders and additives. Results indicate that the surface carboxyl groups introduced by the chemical treatment not only function as the appropriate nucleation sites for Li2O2 but also induce the formation of toroid-like Li2O2. Thus, the surface carboxyl modification enhances the discharge capacities from 0.48 mAh/cm2 of pristine carbon cloth to 1.23 mAh/cm2 of CACC. This work presents an effective way to further optimize the carbonaceous oxygen electrodes via surface functional group engineering

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.

Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions.

The aprotic lithium-oxygen (Li-O2 ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O2 battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O2 battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O2 batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li2 O2 and the mechanisms of Li2 O2 oxidation to O2 on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O2 batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O2 batteries in the future.

The Rechargeable Aprotic Lithium-Oxygen Batteries

Rechargeable battery such as Li-ion battery will be the main focus worldwide for decades to come. However, energy storage beyond the capabilities of Li-ion technologies are becoming increasingly important to satisfy society’s future energy storage needs. One such alternative is aprotic Li-air (O2) battery with its theoretical specific energy several times higher than that of Li-ion. However, many challenges including early cell death, high overpotential and poor cycle life need to be addressed before its commercialisation. Fundamental studies of the processes at the positive electrode have shown that this is a result of passivating Li2O2 film at the electrode surface. It is generally accepted that solution growth of discharge product Li2O2 is required to achieve high rates and capacities. One way to achieve solution mechanism is use of high donor or acceptor number electrolytes, however, such electrolytes are less stable towards the reactive oxygen species in aprotic Li-O2 cell. Here, we discuss our new strategies to use redox mediators as soluble catalysts, to reduce O2 to Li2O2 by halving the overpotential on discharge, without forming passivating films and with less side reactions in ether solvents, while on charge Li2O2 can be oxidized rapidly to O2 even when the former is not in contact with the electrode surface, Fig. 1. As a result, cycling of an aprotic Li-O2 cell has been demonstrated with rates and capacities of several mA and mAh cm-2 respectively. The advantages and disadvantages of redox mediators during cycling and decomposition of carbon electrode will be discussed. Figure 1: Schematics of positive electrode reactions on discharge and charge in the presence of dual mediators. Figure 1

Free-Standing Three-Dimensional CuCo2S4 Nanosheet Array with High Catalytic Activity as an Efficient Oxygen Electrode for Lithium–Oxygen Batteries

In this work, a novel free-standing CuCo2S4 nanosheet cathode (CuCo2S4@Ni) with high catalytic activity is fabricated for aprotic lithium-oxygen (Li-O2) battery. This deliberately designed oxygen electrode is found to yield lower overpotential (0.82 V), improved specific capacity (9673 mA h g-1 at 100 mA g-1), and enhanced cycle life (164 cycles) as compared to the traditional carbonaceous electrode. The improved performance can be ascribed to the superb spinel structure of CuCo2S4, in which both Cu and Co exhibit more abundant redox properties, improving oxygen reduction reaction and oxygen evolution reaction kinetics effectively and boosting the electrochemical reactions. Furthermore, the well-designed architecture also plays a critical role in the improved performance. Encouraged by the excellent catalytic activity of this free-standing cathode, large-scale pouch-type Li-O2 cell based on CuCo2S4@Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li-O2 batteries with excellent performance and flexible wearable devices.

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.

Oxygen-enriched carbon nanotubes as a bifunctional catalyst promote the oxygen reduction/evolution reactions in Li-O2 batteries

The aprotic lithium-oxygen (Li-O2) batteries based on carbon-based oxygen cathodes usually suffer from low round-trip efficiency. Here we adopt oxygen-enriched carbon nanotubes (CNTs) by acid etching treatment as the cathode, in which a low voltage plateau at ∼3.5 V during charge is exhibited and the initial round-trip efficiency is increased from 69.9% to 76.0%. An optimized integration of electrocatalytic property and electrical conductivity is crucial for the oxidized CNTs cathode to enhance the capacity and cycling performance. In particular, the surface oxygen groups can facilitate the electrocatalysis of O2 with the enhanced oxygen reduction reaction activity and induce defective lithium peroxide (Li2O2) formation due to their preferential adsorption of O2 on the oxidized CNTs. Compared to the high crystalline Li2O2 toroids, the defective Li2O2 with poor crystallinity could be decomposed at a lower charge potential, contributing to the enhanced round-trip efficiency of Li-O2 batteries.

Controlling Reversible Expansion of Li2O2 Formation and Decomposition by Modifying Electrolyte in Li-O2 Batteries

Summary The aprotic lithium-oxygen (Li-O2) battery has attracted worldwide attention because of its ultrahigh theoretical energy density. However, its practical application is critically hindered by cathode passivation, large polarization, and severe parasitic reactions. Here, we demonstrate an originally designed Ru(II) polypyridyl complex (RuPC) though which the reversible expansion of Li2O2 formation and decomposition can be achieved in Li-O2 batteries. Experimental and theoretical results revealed that the RuPC can not only expand the formation of Li2O2 in electrolyte but also suppress the reactivity of LiO2 intermediate during discharge, thus alleviating the cathode passivation and parasitic reactions significantly. In addition, an initial delithiation pathway can be achieved when charging in turn; thus, the Li2O2 products can be decomposed reversibly with a low overpotential. Consequently, the RuPC-catalyzed Li-O2 batteries exhibited a high discharge capacity, a low charge overpotential, and an ultralong cycle life. This work provides an alternative way of designing the soluble organic catalysts for metal-O2 batteries.

Elucidating Singlet Oxygen Production in Li-Ion and Metal-Air Batteries

At high voltages, Li-ion and Li-air batteries undergo unwanted electrochemical reactions that can permanently decrease the performance of the battery. Recent experiments studying off-gassing from NMC cathodes have yielded different results for the trends of O2, CO2, and CO gas production with varying Ni composition. Studies also disagree on the origin of the elements in the gas. Very recently, it was suggested that not only is Li2CO3 on NMC cathodes responsible for the majority of CO2 production [1] but that singlet oxygen is produced when Li2CO3 is bias above 3.82 V [2]. This and other studies suggest singlet oxygen production as a common degradation pathway in Li-ion, Li-air [3,4], and Na-air [5]. With the use of first principles methods, we attempt to reconcile these experimental works and propose a universal mechanism of singlet oxygen production. We will also discuss a way to experimentally verify our mechanism by varying the electrolyte, which we claim will change the onset potential of singlet oxygen production in a predictable way. [1] 1. Renfrew, S. E. & McCloskey, B. D. Residual Lithium Carbonate Predominantly Accounts for First Cycle CO2and CO Outgassing of Li-Stoichiometric and Li-Rich Layered Transition-Metal Oxides. J. Am. Chem. Soc. (2017). doi:10.1021/jacs.7b08461 [2] 1. Mahne, N., Renfrew, S. E., McCloskey, B. D. & Freunberger, S. A. Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen. Angew. Chemie Int. Ed. (2018). doi:10.1002/anie.201802277 [3] 1. Mahne, N. et al. Singlet oxygen generation as a major cause for parasitic reactions during cycling of aprotic lithium-oxygen batteries. Nat. Energy (2017). doi:10.1038/nenergy.2017.36 [4] 1. Wandt, J., Jakes, P., Granwehr, J., Gasteiger, H. A. & Eichel, R.-A. Lithium–Air Batteries Singlet Oxygen Formationduring the Charging Process of an Aprotic Lithium–Oxygen Battery. [5] 1. Schafzahl, L. et al. Singlet Oxygen during Cycling of the Aprotic Na-O2 Battery. Angew. Chemie Int. Ed. (2017). doi:10.1002/anie.201709351