Nonaqueous Li-O2 Research Articles

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.

Strategies to suppress the shuttle effect of redox mediators in lithium-oxygen batteries

Various strategies can be used to suppress the shuttle effect of redox mediators in non-aqueous Li-O 2 batteries, including electrolyte additives, protective separators, anode coating and cathode modification. Rechargeable lithium-oxygen (Li-O 2 ) batteries are the next generation energy storage devices due to their ultrahigh theoretical capacity. Redox mediators (RMs) are widely used as a homogenous electrocatalyst in non-aqueous Li-O 2 batteries to enhance their discharge capacity and reduce charge overpotential. However, the shuttle effect of RMs in the electrolyte solution usually leads to corrosion of the Li metal anode and uneven Li deposition on the anode surface, resulting in unwanted consumption of electrocatalysts and deterioration of the cells. It is therefore necessary to take some measures to prevent the shuttle effect of RMs and fully utilize the soluble electrocatalysts. Herein, we summarize the strategies to suppress the RM shuttle effect reported in recent years, including electrolyte additives, protective separators and electrode modification. The mechanisms of these strategies are analyzed and their corresponding requirements are discussed. The electrochemical properties of Li-O 2 batteries with different strategies are summarized and compared. The challenges and perspectives on preventing the shuttle effect of RMs are described for future study. This review provides guidance for achieving shuttle-free redox mediation and for designing Li-O 2 cells with a long cycle life, high energy efficiency and highly reversible electrochemical reactions.

Expansion of the Potential Region for Sustained Discharge of Non-aqueous Li-O2 Batteries Using an Oxygen-enriched Carbon Cathode

This study demonstrates that surface modification of a carbon-paper cathode by oxygen functional groups expands the potential region for the sustained discharge of non-aqueous Li-O2 batteries. Expa...

A Solvent-Controlled Oxidation Mechanism of Li2O2 in Lithium-Oxygen Batteries

Summary Long-unresolved discrepancies in the oxidation mechanism of lithium peroxide (Li2O2) impede electrode/electrolyte development for Li-O2 batteries. In this study, we report direct evidence of the formation of soluble LiO2 upon the oxidation of Li2O2 and reveal a strong solvent-controlled Li2O2-oxidation reaction mechanism. We exploit a thin-film rotating ring-disk electrode to show that soluble LiO2 is generated when oxidizing Li2O2 in high-donicity solvent but is absent in low-donicity glyme-based solvent. Synchrotron-based X-ray absorption near-edge structure spectroscopy further proved the presence of LiO2 upon Li2O2 oxidation in high-donicity solvent but not in low-donicity solvent. We show that preferential formation of soluble LiO2 in the high-donicity solvent could account for poor cycling stability, which suggests that strategies that bypass the formation of soluble LiO2 upon Li2O2 oxidation are critical. Our work offers new insights in resolving the discrepancy in Li-O2 charging mechanism and design strategies to achieve efficient and long-life Li-O2 batteries.

Towards Synergistic Electrode-Electrolyte Design Principles for Nonaqueous Li-O[Formula: see text] batteries.

One route toward sustainable land and aerial transportation is based on electrified vehicles. To enable electrification in transportation, there is a need for high-energy-density batteries, and this has led to an enormous interest in lithium-oxygen batteries. Several critical challenges remain with respect to realizing a practical lithium-oxygen battery. In this article, we present a detailed overview of theoretical efforts to formulate design principles for identifying stable electrolytes and electrodes with the desired functionality and stability. We discuss design principles relating to electrolytes and the additional stability challenges that arise at the cathode-electrolyte interface. Based on a thermodynamic analysis, we discuss two important requirements for the cathode: the ability to nucleate the desired discharge product, Li[Formula: see text]O[Formula: see text], and the ability to selectively activate only thisdischarge product while suppressing lithium oxide, the undesired secondary discharge product. We propose preliminary guidelines for determining the chemical stability of the electrode and illustrate the challenge associated with electrode selection using the examples of carbon cathodes and transition metals. We believe that a synergistic design framework for identifying electrolyte-electrode formulations is needed to realize a practical Li-O[Formula: see text] battery.

Cathode Materials and Catalysts for Non-Aqueous Li-O2 Batteries

Cathode Materials and Catalysts for Non-Aqueous Li-O₂ Batteries

A Viewpoint on Heterogeneous Electrocatalysis and Redox Mediation in Nonaqueous Li-O2 Batteries

A Viewpoint on Heterogeneous Electrocatalysis and Redox Mediation in Nonaqueous Li-O₂ Batteries

Vertically aligned carbon nanotube-ruthenium dioxide core-shell cathode for non-aqueous lithium-oxygen batteries

Abstract Exploitation of hierarchical porous carbons is increasingly attractive for high-capacity lithium (Li)-oxygen (O 2 ) battery cathodes. However, their practical applications in non-aqueous electrolytes are limited by poor rechargeability, primarily due to the decomposition of carbon electrode and electrolyte. In this work, we report a vertically aligned carbon nanotube (VACNT)-ruthenium dioxide (RuO 2 ) core-shell (VACNT@RuO 2 ) cathode for non-aqueous Li-O 2 batteries. The cathode is fabricated with VACNT as the core material and hydrous RuO 2 as the shell material, which eliminates the direct contact between the carbon and nucleophilic reactive intermediate species in the electrolyte. In comparison with the VACNT cathode, the VACNT@RuO 2 cathode presents a superior rate capability (3.3-fold less reduction in capacity) and cycling stability (sustainable for 100 cycles), with a maximum capacity as large as 13.2 mAh cm −2 (6600 mAh g electrode −1 ) at 1.0 mA cm −2 . The proposed cathode exhibiting a binder-free and hierarchical core-shell structure is a promising candidate for rechargeable non-aqueous Li-O 2 batteries.

Numerical predictions and experimental verification of Li-O2 battery capacity limits for cathodes with spherical conductors and solid electrolytes

Abstract The capacity limits, local formation of Li 2 O 2 , passivation of active surfaces, and depletion of oxygen by mass transport characteristics in a composite cathode are modeled, numerically simulated, and experimentally evaluated for non-aqueous Li-O 2 batteries employing composites of a solid polymer electrolyte and carbon particles as the cathode, Li metal as the anode, and an ion conductive oxide membrane as the separator. Although the theoretical maximum specific energy of the Li-O 2 battery is known to be 3458 Wh kg −1 cathode , our simulation predicts a maximum specific energy of 1840 Wh kg −1 cathode with an optimized weight ratio of all essential components as well as cathode thickness. A specific energy of 1713 Wh kg −1 cathode is experimentally demonstrated in a cell with a composite cathode of poly(ethylene oxide) electrolyte and Printex carbon nanoparticles with 48% carbon volume and 30 μm thickness. The model also predicts that the incorporation of voids in the cathode can significantly improve the specific energy.

Solvating additives drive solution-mediated electrochemistry and enhance toroid growth in non-aqueous Li-O₂ batteries.

Given their high theoretical specific energy, lithium-oxygen batteries have received enormous attention as possible alternatives to current state-of-the-art rechargeable Li-ion batteries. However, the maximum discharge capacity in non-aqueous lithium-oxygen batteries is limited to a small fraction of its theoretical value due to the build-up of insulating lithium peroxide (Li₂O₂), the battery's primary discharge product. The discharge capacity can be increased if Li₂O₂ forms as large toroidal particles rather than as a thin conformal layer. Here, we show that trace amounts of electrolyte additives, such as H₂O, enhance the formation of Li₂O₂ toroids and result in significant improvements in capacity. Our experimental observations and a growth model show that the solvating properties of the additives prompt a solution-based mechanism that is responsible for the growth of Li₂O₂ toroids. We present a general formalism describing an additive's tendency to trigger the solution process, providing a rational design route for electrolytes that afford larger lithium-oxygen battery capacities.

Computational Investigations of Charge Transport in Non-Aqueous Li-O 2 Batteries

Despite their great promise, there are significant challenges to developing practical Li−air batteries. One is the electrical passivation of the cathode during discharge.[1,2] This occurs because insoluble and insulating Li2O2 produced during discharge builds up as a deposit on the cathode surface and ultimately inhibits charge transfer to the Li2O 2 −electrolyte interface where the electrochemistry occurs. This manifests itself as a “sudden death” (rapid drop in the output potential U) of the discharge at some maximum discharge capacity, Qmax.In this talk, we will discuss the dependence of the maximum discharge capacity Qmaxon the current density, j.[3] We show that a wide range of experiments can be rationalized using a model that accounts for charge transport through tunneling and polarons. We further show that tunneling dominates at the current density of interest.

Mesoporous NiCo2O4 nanoflakes as electrocatalysts for rechargeable Li–O2 batteries

Herein, we report the facile synthesis of mesoporous NiCo(2)O(4) nanoflakes and their application in nonaqueous Li-O(2) batteries as cathode catalysts. The assembled Li-O(2) batteries presented lower overpotentials and enhanced cyclability, which should be attributed to the superior electrocatalytic activity and the mesoporous nanostructure of NiCo(2)O(4).

The Carbon Electrode in Nonaqueous Li–O2 Cells

Carbon has been used widely as the basis of porous cathodes for nonaqueous Li-O(2) cells. However, the stability of carbon and the effect of carbon on electrolyte decomposition in such cells are complex and depend on the hydrophobicity/hydrophilicity of the carbon surface. Analyzing carbon cathodes, cycled in Li-O(2) cells between 2 and 4 V, using acid treatment and Fenton's reagent, and combined with differential electrochemical mass spectrometry and FTIR, demonstrates the following: Carbon is relatively stable below 3.5 V (vs Li/Li(+)) on discharge or charge, especially so for hydrophobic carbon, but is unstable on charging above 3.5 V (in the presence of Li(2)O(2)), oxidatively decomposing to form Li(2)CO(3). Direct chemical reaction with Li(2)O(2) accounts for only a small proportion of the total carbon decomposition on cycling. Carbon promotes electrolyte decomposition during discharge and charge in a Li-O(2) cell, giving rise to Li(2)CO(3) and Li carboxylates (DMSO and tetraglyme electrolytes). The Li(2)CO(3) and Li carboxylates present at the end of discharge and those that form on charge result in polarization on the subsequent charge. Li(2)CO(3) (derived from carbon and from the electrolyte) as well as the Li carboxylates (derived from the electrolyte) decompose and form on charging. Oxidation of Li(2)CO(3) on charging to ∼4 V is incomplete; Li(2)CO(3) accumulates on cycling resulting in electrode passivation and capacity fading. Hydrophilic carbon is less stable and more catalytically active toward electrolyte decomposition than carbon with a hydrophobic surface. If the Li-O(2) cell could be charged at or below 3.5 V, then carbon may be relatively stable, however, its ability to promote electrolyte decomposition, presenting problems for its use in a practical Li-O(2) battery. The results emphasize that stable cycling of Li(2)O(2) at the cathode in a Li-O(2) cell depends on the synergy between electrolyte and electrode; the stability of the electrode and the electrolyte cannot be considered in isolation.

Li–O2 Battery with a Dimethylformamide Electrolyte

Stability of the electrolyte toward reduced oxygen species generated at the cathode is a crucial challenge for the rechargeable nonaqueous Li-O(2) battery. Here, we investigate dimethylformamide as the basis of an electrolyte. Although reactions at the O(2) cathode on the first discharge-charge cycle are dominated by reversible Li(2)O(2) formation/decomposition, there is also electrolyte decomposition, which increases on cycling. The products of decomposition at the cathode on discharge are Li(2)O(2), Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li, NO, H(2)O, and CO(2). Li(2)CO(3) accumulates in the electrode with cycling. The stability of dimethylformamide toward reduced oxygen species is insufficient for its use in the rechargeable nonaqueous Li-O(2) battery.