Lithium Oxygen Cells Research Articles

Synergistic effect of oxygen vacancies and in-situ formed bismuth metal centers on BiVO4 as an enhanced bifunctional Li–O2 batteries electrocatalyst

Bismuth Vanadate (BiVO4) is a promising oxide-based photoanode for electrochemical applications, yet its practical use is constrained by poor charge transport properties, particularly under dark conditions. This study introduces a novel BiVO4 variant (Bi-BiVO4-10) that incorporates abundant oxygen vacancies and in-situ formed Bi metal, significantly enhancing its electrical conductivity and catalytic performance. Bi-BiVO4-10 demonstrates superior electrochemical performances compared to conventional BiVO4 (C-BiVO4), demonstrated by its most positive half-wave potential with the highest diffusion-limiting current in the oxygen reduction reaction (ORR) and earliest onset potential in the oxygen evolution reaction (OER). Notably, Bi-BiVO4-10 is explored for the first time as an electrocatalyst for lithium-oxygen (Li–O2) cells, showing reduced overcharge (610 mV) in the first cycle and extended cycle life (1050 h), outperforming carbon (320 h) and C-BiVO4 (450 h) references. The enhancement is attributed to the synergy of oxygen vacancies, Bi metal formation, increased surface area, and improved electrical conductivity, which collectively facilitate Li2O2 growth, enhance charge transport kinetics, and ensure stable cycling. Theoretical calculations reveal enhanced chemical interactions between intermediate molecules and the defect-rich surfaces of Bi-BiVO4-10, promoting efficient discharge and charge processes in Li–O2 batteries. This research highlights the potential of unconventional BiVO4-based materials as durable electrocatalysts and for broader electrochemical applications.

Phthalocyanine-based bifunctional soluble hybrid catalyst for rechargeable lithium-oxygen batteries

A mixture of tetrabutylammonium lithium phthalocyanine (TBA-LiPc) and dilithium phthalocyanine (Li2Pc) (2:1 mol ratio) functions as a bifunctional soluble hybrid catalyst in tetraethylene glycol dimethyl ether (TEGDME) for a rechargeable lithium-oxygen cell. Cyclic voltammetry (CV) measurements of the hybrid catalyst in TEGDME show highly symmetrical peaks at 2.54 V and 3.22 V vs Li/Li+ corresponding to oxygen reduction and oxygen oxidation reactions, respectively. Long-term cycling of cells with PVP-modified graphene nanosheets (GNSs) coated hierarchical porous carbons (HPC) cathodes at a fixed capacity of 1200 mAh/g (carbon) exhibits 402 and 379 cycles in oxygen and dry-air, respectively.

Quantitative elucidation of cathode reaction mechanisms in Li-O₂ batteries within high donor number solvents

Lithium-oxygen cells, known for their exceptional energy density, have complex reaction processes making a quantitative elucidation of the reaction mechanism, especially at the cathode quite difficult. Using density functional theory (DFT) combined with nudged elastic band (NEB) calculations, and cyclic voltammetry (CV) experiments in high donor number solvents, we developed a numerical computational model that elucidates the primary reaction pathway at the cathode. This study highlights two key reasons for the voltage gap between the charging and discharging phases: the shift in lithium superoxide's reaction voltage from lithium peroxide's thermodynamic equilibrium voltage, and the extra energy needed to electrolyze nucleated lithium peroxide. This study shows that by optimizing the high donor number solvent system and optimum battery design, up to 78.9 % of theoretical specific energy can be achievable, signaling significant prospects for advancing Li-O₂ battery technology.

Phthalocyanine as catalyst for rechargeable lithium-oxygen batteries

Tetrabutylammonium lithium phthalocyanine (TBA-LiPc) can function as a soluble catalyst in low-donor-number (DN) solvents such as tetraethylene glycol dimethyl ether (TEGDME) (DN=16.6) for rechargeable lithium-oxygen cells. It is able to do so given that molecular oxygen forms a complex with the lithium phthalocyanine anion thereby keeping oxygen and the reaction intermediates in solution. Density functional theory (DFT) calculations show the mechanism for complex formation and cyclic voltammetry results support the notion of reaction intermediates that are soluble in solution during oxygen reduction and oxygen evolution reactions. Deep discharge of a lithium-oxygen cell with TBA-LiPc had a capacity that was 3.6 times greater (5.28 mAh) than a similar cell with no TBA-LiPc (1.47 mAh). Long-term cycling of a lithium-oxygen cell with TBA-LiPc at a fixed capacity of 0.55 mAh did not fail after 100 cycles. A similar cell without TBA-LiPc failed after 37 cycles. Long-term cycling of a lithium-oxygen cell with TBA-LiPc and using natural air in low humidity as the source of oxygen cycled 151 times before cell failure.

Singlet oxygen and dioxygen bond cleavage in the aprotic lithium-oxygen battery

<h2>Summary</h2> Investigation of lithium-oxygen cells on discharge using a mixture of ¹⁶O¹⁶O and ¹⁸O¹⁸O gases, showed that O–O bond cleavage occurs during disproportionation of LiO₂ to O₂ and Li₂O₂, detected by the presence of isotopic ¹⁶O¹⁸O. The formation of singlet oxygen, ¹O₂, was also monitored during disproportionation. While only 4.5% of oxygen was found to undergo bond cleavage and scrambling of oxygen atoms, more than 40% of the singlet oxygen produced during disproportionation came from the scrambling pathway, making it a major source of singlet oxygen generation in lithium-oxygen batteries. Our results demonstrate that Li₂O₂ formation occurs predominantly by disproportionation, and by controlling the pathway of this step, it may be possible to suppress ¹O₂ formation, a species that has been implicated in the degradation of lithium-oxygen batteries.

Gas Analysis of Ether-Based Electrolytes in Lithium-Oxygen Cells

Low-cost cell chemistries like metal-oxygen batteries are an essential component of future energy storage systems. Due to its very high theoretical energy density the system lithium-oxygen (Li-O2) is an interesting candidate.Gas analytical studies of Li-O2 cells with ether-based electrolytes are presented. The electrolytes used consist of 1M LiTFSI in DEGDME respectively TEGDME. The focus is on investigations of non-linear ageing processes such as electrolyte decomposition during cycling. All measurements were carried out using specially developed multifunctional test setups and accordingly modified test cells. Li-O2 measurements at different O2-flow rates were examined by GC-MS and in-operando MS.Next-generation battery systems typically suffer from severe gassing, which causes a loss of electrolyte and finally the cell to dry out. Consequently, the cycling stability is strongly limited. Gas analysis is a suitable method to identify decomposition and ageing reactions, to benchmark and to define operating parameters. With the GC-MS, a post-mortem analysis could be performed to identify the individual substances qualitatively. In addition, in-operando MS could be used to detect gaseous substances produced by (electro)chemical processes as a function of the state of charge.As major results, the cyclic formation of several degradation products can be demonstrated. CO2, hydrogen as well as methanol, methyl formate, methylal and 1,3-dioxolane were identified as characteristic decomposition products of DEGDME. Furthermore, the presence of many other oxygenated organic compounds can be detected, making it possible to trace the stepwise degradation of DEGDME as a function of the state of charge.These analytical studies make an important contribution to the understanding of the reaction mechanism and ageing reactions in Li-O2 cells with ether-based electrolyte. As a consequence, the shown results help to develop appropriate countermeasures in order to reduce the negative effects mentioned above and thus to ensure a higher cycling stability.This work is funded by the German Federal Ministry of Education and Research (BMBF) in the project “Osaban” (03XP0227B) which is part of the German-Japanese battery cooperation program. The project partners are University of Kyoto (Japan) and Justus-Liebig-University Gießen (Germany). Figure 1

PMMA-LiTFSI based gel polymer electrolyte for lithium-oxygen cell application

In this work, poly (methyl methacrylate), PMMA based gel polymer electrolytes (GPEs) have been studied. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was selected as lithium-ion donor and tetraethylene glycol dimethyl ether (TEGDME) as a solvent. The highest conducting sample was obtained at 25 wt% LiTFSI with ionic conductivity value of 2.80 mS cm −1 . The dielectric constant of GPEs sample follows the conductivity trend. The percentage of free ions is observed to increase up to electrolyte containing 25 wt% LiTFSI salt. Beyond that, the free ions percentage decreased. Lithium-ion transference number for the highest conducting sample is 0.47. The highest ionic conducting sample show good electrode-electrolyte interfacial stability and is suggested suitable in lithium-oxygen batteries. The charge and discharge capacities in the first cycle were 0.87 and 1.23 mAh cm −2 , respectively. Formation of Li 2 O 2 can be observed by XRD pattern of the air cathode during the discharge. • Large anion size contributes to enhance the ionic conductivity and lithium transference number. • A gel polymer electrolyte based on PMMA is a viable candidate for use as the electrolyte in a lithium-oxygen battery. • The discharge capacity retention of lithium-oxygen cell is 26 % after five cycles.

Liquid‐Based Janus Electrolyte for Sustainable Redox Mediation in Lithium–Oxygen Batteries

AbstractThe discovery of a reliable electrolyte system remains one of the key challenges for the development of advanced lithium–oxygen batteries. To date, no single electrolyte is verified to be stable and compatible with both the cathode (e.g., oxygen radicals, lithium peroxide, etc.) and anode (lithium metal) for lithium–oxygen batteries. In this work, a novel liquid‐based Janus electrolyte system consisting of two different immiscible liquid phases is proposed and it is demonstrated that this system is remarkably effective in promoting the sustainable operation of redox‐mediated lithium–oxygen batteries. The liquid‐based Janus electrolyte is rationally designed by considering its compatibility with the lithium–oxygen cell environment, the solubility difference of target soluble species, and the mutual immiscibility of the two liquid phases. By combining spectral characterization, a phase‐separation experiment, and in situ observation of the electrochemical cell, it is revealed that the liquid‐based Janus electrolyte suppresses the migration of redox mediators from one liquid phase to the other, thereby preventing the detrimental shuttle effect. The enhanced stability of redox mediation leads to improved cycling performance of the cell. The various combinations possible for the liquid‐based Janus electrolyte open a new unexplored pathway for the design of advanced electrolyte systems for lithium–oxygen batteries.

First-Principles Study of the Surfaces and Equilibrium Shape of Discharge Products in Li-Air Batteries.

Li-air batteries are a promising alternative to Li-ion batteries as they theoretically provide the highest possible specific energy density. Mainly, Li2O2 (lithium peroxide) and to a lesser extent, Li2O (lithium oxide) are assumed to be the discharge products of these batteries formed with the soluble LiO2 (lithium superoxide) considered to be an intermediate product. Bulk Li2O2 is an electronic insulator, and the precipitation of this compound on the cathode is thought to be the main limiting factor in achieving high capacities in lithium-oxygen cells. For the most promising electrolytes including solvents with high donor numbers, microscopy observations frequently reveal crystallite morphologies of Li2O2 compounds, rather than uniform layers covering the electrode surface. The precise morphologies of Li2O and Li2O2 particles, and their effect and their extent of contact with the electrode, which may all affect the capacity and rechargeability, however, remain largely undetermined. Here, we address the stability of various Li2O and Li2O2 surfaces and consequently, their crystallite morphologies using density functional theory calculations and ab initio thermodynamics. In contrast to previous studies, we also consider high-index surface terminations, which exhibit surprisingly low surface energies. We carefully analyze the reasons for the stability of these high-index surfaces, which also prominently influence the equilibrium shape of the particles, at least for Li2O2, and discuss the consequences for the observed morphology of the reaction products.

Improved Electrocatalytic Activity of Three-Dimensional Open-Structured Co3O4@MnO2 Bifunctional Catalysts of Li-O2 Batteries by Inducing the Oriented Growth of Li2O2

Rational structure and morphology design of catalytic cathode materials is the key to realize excellent performances of lithium-oxygen batteries (LOBs). Herein, a three-dimensional (3D) open-structured Co₃O₄@MnO₂ heteromatrix has been designed through a facile two-step hydrothermal method. Unexpectedly, when it serves as oxygen reduction reaction/oxygen evolution reaction bifunctional catalytic cathodes for lithium-oxygen cells, the 3D open-structured Co₃O₄@MnO₂ heteromatrix-catalyzed LOBs exhibit outstanding electrochemical performances (a high specific capacity of 12,980 mA h g–¹ during the initial discharge and long cycle life of 331, 197, and 14 times with specific capacities fixed at 500, 1000, and even 3000 mA h g–¹, respectively), obviously superior to reported batteries based on low-dimensional and closed-ended catalysts. We find that the enhanced electrochemical performances are ascribed to the bifunctional catalyst and the 3D open structure of the Co₃O₄@MnO₂ heteromatrix, which can guide the homogeneous and fluffy deposition of discharge products Li₂O₂, demonstrating a promising application in both LOBs and flexible/wearable Li-air batteries.

Anchored Mediator Enabling Shuttle–Free Redox Mediation in Lithium–Oxygen Batteries

Redox mediators (RMs) are considered an effective countermeasure to reduce the large polarization in lithium–oxygen batteries. Nevertheless, achieving sufficient enhancement of the cyclability is limited by the trade–offs of freely mobile RMs, which are beneficial for charge transport but also trigger the shuttling phenomenon. Here, we successfully decoupled the charge–carrying redox property of RMs and shuttling phenomenon by anchoring the RMs in polymer form, where physical RM migration was replaced by charge transfer along polymer chains. Using a model system of a polymer, PTMA (2,2,6,6–tetramethyl–1–piperidinyloxy–4–yl methacrylate), based on the well–known RM tetramethylpiperidinyloxyl (TEMPO), it is demonstrated that PTMA is capable of functioning as a stationary RM, preserving the redox activity of TEMPO. The efficiency of RM–mediated Li2O2 decomposition remains remarkably stable without the consumption of oxidized RMs or degradation of the lithium anode, resulting in marked improvement of the performance of the lithium–oxygen cell.

Ionic liquid-based gel polymer electrolyte containing zwitterion for lithium-oxygen batteries

The key challenge of high energy density lithium-oxygen batteries is to develop a stable electrolyte system not only to suppress growth of lithium dendrite and solvent evaporation but also to resist the attack by superoxide anion radical formed at the cathode. Gel polymer electrolyte can effectively encapsulate organic solvent in the cell, suppress electrolyte decomposition and provide stable interfacial characteristics with lithium electrode. In this study, a three-dimensional cross-linked poly(methyl methacrylate)-based gel polymer electrolyte (GPE) containing non-volatile ionic liquid and zwitterion was synthesized and characterized for lithium-oxygen batteries. In this GPE, a zwitterion was proved to improve the transport properties of Li+ ions and enhance the interfacial stability towards the lithium electrode. As a result, the lithium-oxygen cell assembled with GPE containing ionic liquid and zwitterion exhibited a good cycling stability at a constant current density of 0.25 mA cm−2.

Anchored Mediator Enabling Shuttle-Free Redox Mediation in Lithium-Oxygen Batteries.

Redox mediators (RMs) are considered an effective countermeasure to reduce the large polarization in lithium-oxygen batteries. Nevertheless, achieving sufficient enhancement of the cyclability is limited by the trade-offs of freely mobile RMs, which are beneficial for charge transport but also trigger the shuttling phenomenon. Here, we successfully decoupled the charge-carrying redox property of RMs and shuttling phenomenon by anchoring the RMs in polymer form, where physical RM migration was replaced by charge transfer along polymer chains. Using PTMA (poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate)) as a polymer model system based on the well-known RM tetramethylpiperidinyloxyl (TEMPO), it is demonstrated that PTMA can function as stationary RM, preserving the redox activity of TEMPO. The efficiency of RM-mediated Li2 O2 decomposition remains remarkably stable without the consumption of oxidized RMs or degradation of the lithium anode, resulting in an improved performance of the lithium-oxygen cell.

Trace fluorinated-carbon-nanotube-induced lithium dendrite elimination for high-performance lithium-oxygen cells.

Lithium metal has attracted considerable attention due to its ultrahigh theoretical capacity. Nevertheless, issues such as dendritic Li formation and instability of the Li metal/electrolyte interface still restrain its practical applications. In this work, we design a Li composite anode with fluorinated carbon nanotubes (FCNT) fabricated by a simple melting-soaking method. It was found that trace amounts of added FCNT (only 1.6 wt%) lead to a significant chemical/electrochemical stability of metallic Li. The obtained Li/FCNT composite electrode (LFCNT) exhibits much better stability in open air and electrolyte than bare Li. The LFCNT enables uniform plating/stripping of metallic Li, preventing the dendrite formation during repeated cycling. In situ optical microscopy observations confirm dendrite-free Li deposition with the mechanism clarified by density functional theory calculations. Compared with bare Li, the LFCNT shows a considerable improvement in rate capability, voltage hysteresis and cycle performance, sustaining stable cycling at a high current density of 3 mA cm-2 or a capacity up to 5 mA h cm-2. Li-O2 cells with a LFCNT anode exhibit a long life of 135 cycles at a capacity of 1000 mA h g-1, which is six-fold than that with the bare Li anode.

Dendrite-Free Fluorinated Graphene/Lithium Anodes Enabling in Situ LiF Formation for High-Performance Lithium-Oxygen Cells.

Metallic Li is considered as the ultimate choice of negative electrodes for Li batteries because of its largest theoretical specific capacity. However, formidable issues such as poor safety and cyclability caused by lithium dendrite growth and tremendous interfacial side reactions have strictly hindered its practical applications. Here, we report a fluorinated graphene (FG)-modified Li negative electrode (LFG) for high-performance lithium-oxygen (Li-O2) cells. The results show that only 3 wt % FG introduction leads to a significant enhancement on rate capability and cycling life of Li electrodes. Compared with the half cells with bare Li, the cells with LFG exhibit much more stable voltage profiles even at a large areal capacity up to 5 mA h cm-2 or a large current density up to 5 mA cm-2. Li-O2 cells with the LFG anode show a longer cycle life than the cell with the pristine lithium anode. It was found that a LiF-rich layer could be in situ built upon cycling when FG was used, which ensures uniform Li stripping/plating and effectively suppresses Li dendrite growth. Density functional theory calculations confirm the possibility of conversion from FG to graphene and LiF after Li intercalation into LFG during cycling. In situ optical microscopy observation vividly exhibits the obvious inhibition effect of FG for Li dendrite growth.

Building high performance silicon–oxygen and silicon–sulfur battery by in-situ lithiation of fibrous Si/C anode

Using Li metal-free anodes for lithium-ion oxygen and lithium-ion sulfur batteries is considered as a promising solution to resolve the hazard of Li metal anode. Although Si anode exhibits high capacity and low electrochemical potential, it cannot match with oxygen (or sulfur) cathode, because both lack cycleable lithium ions. In this work, a free-standing and fibrous Si/C anode is prepared by electrospinning and its simple but effective lithiation is proposed. When assembling the cells, the free-standing Si/C anode was put between mass-controlled lithium metal foil and separator, and then the Si/C anode could be lithiated after adding electrolytes. By optimizing a LiFSI based ether electrolyte, the Si/C anode could achieve good cycleablity comparable to that in carbonate electrolytes. The lithiated Si–O2 cells exhibit better cycling stability than the lithium oxygen cells with gel polymer electrolye. Moreover, because both Si anode and S@pPAN cathode are compatible with carbonate electrolytes, exceptional cycling performance has been achieved for the lithiated Si–S cells. This simple method could pave the way to commercial applications of lithium-ion oxygen and lithium-ion sulfur batteries.

Realizing discrete growth of thin Li2O2 sheets on black phosphorus quantum dots-decorated δ-MnO2catalyst for long-life lithium–oxygen cells

Lithium–oxygen (Li–O2) cells have attained increasing attention in recent years due to their extremely high energy density. An efficient catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a key factor for high-performance Li–O2 cells. In this work, a unique design of catalytic cathode composed of black phosphorus quantum dots-decorated δ-MnO2 nanobelts (BPQD/δ-MnO2) on carbon cloth is proposed. The thin belt-like architecture of δ-MnO2 and porous structure of the catalytic cathode not only provide numerous catalytic sites for ORR/OER but also facilitate transportation of the reactants and deposition of the discharge product. The synergic effect of δ-MnO2 and BPQD enables discrete growth of thin Li2O2 sheets on δ-MnO2, leading to high capacity (8463 mAh g−1 at 100 mA g−1) and long cycle life (182 cycles at 400 mA g−1 with a limited capacity of 1000 mAhg−1) of the cells. Density functional theory calculations support that Li2O2 favors conformal growth on δ-MnO2 in the presence of BPQD.

Centrifugal Field Guided Dual Templating Synthesis of Functional Macro‐Microporous Carbon

AbstractDue to the important role of porous carbon in the development of sustainable materials, the synthesis of porous carbon materials with various pore structures and pore sizes is intensively developed. But it is still not an easy task to obtain uniform porous structures at different nanoscales, let alone the hierarchical structures which combine different uniform porosity. The objective of this paper is to investigate if centrifugal field is applicable in the synthesis of ordered macro‐microporous carbon structures and the performance of the obtained porous carbon used as the cathode of a lithium–oxygen cell. It is found that a centrifugal force can trap the nucleation and growth of ZIF‐8 nanocrystals in between the interstices of close‐packed polymeric spheres, and therefore result in ordered macro‐microporous carbon nanoparticles with smaller pores distributed in the wall of larger pores. The dual porosity structures significantly help the macro‐microporous carbon to deliver a much higher capacity when used as the cathodes of a lithium–oxygen battery.

Optimization of Li-O2 Batteries Using Bi Compartment Cells to Separate and Improve Each Electrode Condition

Despite theoretically high energy density of Li-O2 batteries, low energy efficiency, poor cycle life and Li-metal safety issues make the use of them yet impractical. Therefore, efforts are made to protect/block the lithium metal anode in these cells, in order to mitigate side reactions. However, new approach1-3 is required in order to solve the problems mentioned above, especially the irreversible reactions of the redox mediators which are mandatory to these systems with the Li anode. Here, optimized bi compartment cells are proposed, in which detrimental crossover between the cathode and anode is completely avoided. The Li metal anode is cycled in electrolyte solution containing fluorinated ethylene carbonate, in which its cycling efficiency is excellent. The cathode compartment contains ethereal solution with redox mediator that enables oxidation of Li2O2 at low potentials. The electrodes are separated by a solid electrolyte membrane, allowing free transport of Li ions. This approach increases cycle life of lithium oxygen cells and their energy efficiency.1 References W.-J. Kwak, H.-G. Jung, D. Aurbach, and Y.-K. Sun, Adv. Energy Mater. 2017, 7, 1701232 S. H. Lee, J.-B. Park, H.-S. Lim, and Y.-K. Sun, Adv. Energy Mater. 2017 , 7, 1602417 W.-J. Kwak, S.-J. Park, H.-G. Jung, and Y.-K. Sun, Adv. Energy Mater. 2017, 7, 1702258

Kinetics of lithium peroxide oxidation by redox mediators and consequences for the lithium\u2013oxygen cell

Lithium–oxygen cells, in which lithium peroxide forms in solution rather than on the electrode surface, can sustain relatively high cycling rates but require redox mediators to charge. The mediators are oxidised at the electrode surface and then oxidise lithium peroxide stored in the cathode. The kinetics of lithium peroxide oxidation has received almost no attention and yet is crucial for the operation of the lithium–oxygen cell. It is essential that the molecules oxidise lithium peroxide sufficiently rapidly to sustain fast charging. Here, we investigate the kinetics of lithium peroxide oxidation by several different classes of redox mediators. We show that the reaction is not a simple outer-sphere electron transfer and that the steric structure of the mediator molecule plays an important role. The fastest mediator studied could sustain a charging current of up to 1.9 A cm–2, based on a model for a porous electrode described here.