Li-air Research Articles

Bimetallic phosphide wrapped in hierarchically structured P, N co-doped porous carbon nanocatalysts for enhanced rechargeable Li[sbnd]O2 batteries

Recently, transition-metal phosphides (TMPs) cathode materials possess tremendous prospects for lithium‑oxygen batteries (LOBs). However, designing highly efficient TMPs cathode materials achieving long-cycling stability still faces numerous obstacles. The hierarchical porous carbon is expected to be a remarkable substrate for transition-metal composites because of its high specific surface area and superior electrical conductivity. Herein, NiCoP@PNC hybrid catalysts consisting of NiCoP nanoparticles and heteroatom-doped carbon skeleton were prepared via simple freeze-drying and high-temperature pyrolysis methods. The NiCoP@PNC composites with a high specific surface area and rich interior porosity can effectively accelerate charge transfer and enhance electrocatalytic activity. Compared with either Co2P@PNC and PNC electrodes, the NiCoP@PNC cathode delivers an enhanced specific capacity of 14,028.1 mAh g−1 at 100 mA g−1. The NiCoP@PNC catalytic LOBs can reach 196 cycles with the fixed capacities of 500 mAh g−1 at 200 mA g−1 due to the increased electron transfer efficiency and improved electrochemical reaction kinetics. This approach provides a facile method to prepare TMP-based composite materials for developing high-performance LOBs.

Solution-Plasma Synthesis and Characterization of Transition Metals and N-Containing Carbon-Carbon Nanotube Composites.

Lithium-air batteries (LABs) have a theoretically high energy density. However, LABs have some issues, such as low energy efficiency, short life cycle, and high overpotential in charge-discharge cycles. To solve these issues electrocatalytic materials were developed for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which significantly affect battery performance. In this study, we aimed to synthesize electrocatalytic N-doped carbon-based composite materials with solution plasma (SP) using Co or Ni as electrodes from organic solvents containing cup-stacked carbon nanotubes (CSCNTs), iron (II) phthalocyanine (FePc), and N-nethyl-2-pyrrolidinone (NMP). The synthesized N-doped carbon-based composite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). TEM observation and XPS measurements revealed that the synthesized carbon materials contained elemental N, Fe, and electrode-derived Co or Ni, leading to the successful synthesis of N-doped carbon-based composite materials. The electrocatalytic activity for ORR of the synthesized carbon-based composite materials was also evaluated using electrochemical measurements. The electrochemical measurements demonstrated that the electrocatalytic performance for ORR of N-doped carbon-based composite material including Fe and Co showed superiority to that of N-doped carbon-based composite material including Fe and Ni. The difference in the electrocatalytic performance for ORR is discussed regarding the difference in the specific surface area and the presence ratio of chemical bonding species.

Lattice Boltzmann Simulations of Non-Homogeneous Li–O2 Battery Cathode: The Effect of Spatial and Temporal Porosity Variations

Abstract The porosity of the cathode in a lithium–oxygen battery is a crucial parameter that influences oxygen transport and active surface area availability. This study explores various cathode models with different initial porosity distributions and analyzes the porosity evolution during discharge. The objective is to maximize the active surface area utilization of the cathode and increase the battery’s discharge capacity. The simulations employ a recently developed lattice Boltzmann method (LBM) model proposed by Chen et al. (2017, “Simulation of Double Diffusive Convection in Fluid-Saturated Porous Media by Lattice Boltzmann Method,” Int. J. Heat Mass Transfer, 108, pp. 1501–1510), which is capable of handling spatial and temporal variations in diffusion coefficient values. The results demonstrate that a hierarchical porous cathode provides a better specific capacity than a uniform porous cathode with the same average initial porosity. The specific capacity increases as the magnitude of initial porosity variation in the domain increases. Furthermore, incorporating oxygen channels improves oxygen transport in the cathode and offers a better specific capacity than the hierarchical porous cathode. A combination of hierarchical porous media and oxygen channels delivers the best specific capacity among all the other cathode models, as it efficiently balances oxygen transport and active surface area.

Aprotic Lithium-Oxygen Batteries Based on Nonsolid Discharge Products.

Aprotic lithium-oxygen (Li-O2) batteries are considered to be a promising alternative option to lithium-ion batteries for high gravimetric energy storage devices. However, the sluggish electrochemical kinetics, the passivation, and the structural damage to the cathode caused by the solid discharge products have greatly hindered the practical application of Li-O2 batteries. Herein, the nonsolid-state discharge products of the off-stoichiometric Li1-xO2 in the electrolyte solutions are achieved by iridium (Ir) single-atom-based porous organic polymers (termed as Ir/AP-POP) as a homogeneous, soluble electrocatalyst for Li-O2 batteries. In particular, the numerous atomic active sites act as the main nucleation sites of O2-related discharge reactions, which are favorable to interacting with O2-/LiO2 intermediates in the electrolyte solutions, owing to the highly similar lattice-matching effect between the in situ-formed Ir3Li and LiO2, achieving a nonsolid LiO2 as the final discharge product in the electrolyte solutions for Li-O2 batteries. Consequently, the Li-O2 battery with a soluble Ir/AP-POP electrocatalyst exhibits an ultrahigh discharge capacity of 12.8 mAh, an ultralow overpotential of 0.03 V, and a long cyclic life of 700 h with the carbon cloth cathode. The manipulation of nonsolid discharge products in aprotic Li-O2 batteries breaks the traditional growth mode of Li2O2, bringing Li-O2 batteries closer to being a viable technology.

Template assisted lithium superoxide growth for lithium-oxygen batteries.

Developing batteries with energy densities comparable to internal combustion technology is essential for a worldwide transition to electrified transportation. Li-O2 batteries are seen as the 'holy grail' of battery technologies since they have the highest theoretical energy density of all battery technologies. Current lithium-oxygen (Li-O2) batteries suffer from large charge overpotentials related to the electronic resistivity of the insulating lithium peroxide (Li2O2) discharge product. One potential solution is the formation and stabilization of a lithium superoxide (LiO2) discharge intermediate that exhibits good electronic conductivity. However, LiO2 is reported to be unstable at ambient temperature despite its favorable formation energy at -1.0 eV per atom. In this paper - based on our recent work on the development of cathode materials for aprotic lithium oxygen batteries including two intermetallic compounds, LiIr3 and LiIr, that are found to form good template interfaces with LiO2 - a simple goodness of fit R factor to gauge how well a template surface structure can support LiO2 growth, is developed. The R factor is a quantitative measurement to calculate the geometric difference in the unit cells of specific Miller Index 2D planes of the template surface and LiO2. Using this as a guide, the R factors for LiIr3, LiIr, and La2NiO4+δ, are found to be good. This guide is attested by simple extension to other noble metal intermetallics with electrochemical cycling data including LiRh3, LiRh, and Li2Pd. Finally, the template concept is extended to main group elements and the R factors for LiO2 (111) and Li2Ca suggest that Li2Ca is a possible candidate for the template assisted LiO2 growth strategy.

A lithium-air battery and gas handling system demonstrator.

The lithium-air (Li-air) battery offers one of the highest practical specific energy densities of any battery system at >400 W h kgsystem-1. The practical cell is expected to operate in air, which is flowed into the positive porous electrode where it forms Li2O2 on discharge and is released as O2 on charge. The presence of CO2 and H2O in the gas stream leads to the formation of oxidatively robust side products, Li2CO3 and LiOH, respectively. Thus, a gas handling system is needed to control the flow and remove CO2 and H2O from the gas supply. Here we present the first example of an integrated Li-air battery with in-line gas handling, that allows control over the flow and composition of the gas supplied to a Li-air cell and simultaneous evaluation of the cell and scrubber performance. Our findings reveal that O2 flow can drastically impact the capacity of cells and confirm the need for redox mediators. However, we show that current air-electrode designs translated from fuel cell technology are not suitable for Li-air cells as they result in the need for higher gas flow rates than required theoretically. This puts the scrubber under a high load and increases the requirements for solvent saturation and recapture. Our results clarify the challenges that must be addressed to realise a practical Li-air system and will provide vital insight for future modelling and cell development.

Evaluation of performance metrics for high energy density rechargeable lithium-oxygen batteries.

The demand for practical implementation of rechargeable lithium-oxygen batteries (LOBs) has grown owing to their extremely high theoretical energy density. However, the factors determining the performance of cell-level high energy density LOBs remain unclear. In this study, LOBs with a stacked-cell configuration were fabricated and their performance evaluated under different experimental conditions to clarify the unique degradation phenomenon under lean-electrolyte and high areal capacity conditions. First, the effect of the electrolyte amount against areal capacity ratio (E/C) on the battery performance was evaluated, revealing a complicated voltage profile for an LOB cell operated under high areal capacity conditions. Second, the impact of different kinds of gas-diffusion layer materials on the "sudden death" phenomenon during the charging process was investigated. The results obtained in the present study reveal the importance of these factors when evaluating the performance metrics of LOBs, including cycle life, and round-trip energy efficiency. We believe that adopting a suitable experimental setup with appropriate technological parameters is crucial for accurately interpreting the complicated phenomenon in LOBs with cell-level high energy density.

First-principles study of catalytic mechanism of boron-doped graphene oxide on oxygen evolution reaction of lithium peroxide

Lithium-oxygen batteries stand out among post-lithium-ion batteries due to their theoretically high energy density, while the sluggish reaction kinetics of lithium peroxide reduces the rate performance of the batteries. Therefore, improving the reaction kinetics of the lithium peroxide and then lowering the charge overpotential are of great importance for realizing reversible lithium-oxygen batteries with high energy density. In this work, the catalytic mechanism of graphene oxide (GO) and boron-doped graphene oxide (BGO) on the oxygen evolution reaction of (Li<sub>2</sub>O<sub>2</sub>)<sub>2</sub> cluster is investigated by first-principles calculations. The results show that the charge transfer from (Li<sub>2</sub>O<sub>2</sub>)<sub>2</sub> cluster to GO and from (Li<sub>2</sub>O<sub>2</sub>)<sub>2</sub> cluster to BGO are 0.59 e and 0.96 e, respectively, suggests that B doping improves the charge transfer from the discharged product to the cathode material. The Gibbs free energy of the 4-electron decomposition process shows that the (Li<sub>2</sub>O<sub>2</sub>)<sub>2</sub> cluster favors the Li-O<sub>2</sub>-Li decomposition pathway, and the rate-determining step for the reaction on both GO and BGO is the third step, that is, the removal of the third lithium. At the equilibrium potential, the charge overpotential of GO and BGO are 0.76 V and 0.23 V, respectively, showing that B doping greatly reduces the charging overpotential of lithium-oxygen batteries. Moreover, mechanistic analysis shows that B doping enhances the electronic conductance of GO and forms an electron-deficient active center, which facilitates charge transport in cathode and charge transfer from lithium peroxide to cathode materials, thereby reducing the charging overpotential of the lithium-oxygen batteries and improving its cycling performance. The B and O play a synergistic role in catalyzing the oxygen evolution reaction of (Li<sub>2</sub>O<sub>2</sub>)<sub>2</sub> clusters.

Dissolved LiO2 or adsorbed LiO2? The reactive superoxide during discharging process in lithium-oxygen batteries.

Lithium-oxygen batteries are promising but have many challenges. Unlike lithium-ion batteries, they are usually discharge-charge cycled with capacity cutoff instead of potential cutoff, which brings controversy. Additionally, which superoxide intermediate, the dissolved or the adsorbed superoxide, is more reactive and leads to cell premature death and unsatisfactory discharge capacity? These questions puzzle researchers and impede the development of lithium-oxygen batteries. Herein, on one hand, we tried to decouple the influence of discharging potential and discharging current density on the discharge products and side reactions. We found that the electrode potential has more impact on the side reactions than the current density. The low potential leads to a high ratio of Li2CO3 to Li2O2 in the discharge product and hence more surface passivation. On the other hand, to identify the more reactive and aggressive species that cause surface passivation, a flow cell setup was applied to suppress the solution route and maximize the products from the surface route. Results show that more Li2CO3 was identified under a large flow rate and thus the intermediates in surface route appear to be more reactive than that in solution route.

A facile coprecipitation approach for synthesizing LaNi0.5Co0.5O3 as the cathode for a molten-salt lithium-oxygen battery.

The cathode of a lithium-oxygen battery (LOB) should be well designed to deliver high catalytic activity and long stability, and to provide sufficient space for accommodating the discharge product. Herein, a facile coprecipitation approach is employed to synthesize LaNi0.5Co0.5O3 (LNCO) perovskite oxide with a low annealing temperature. The assembled LOB exhibits superior electrochemical performance with a low charge overpotential of 0.03-0.05 V in the current density range of 0.1-0.5 mA cm-2. The battery ran stably for 119 cycles at a high coulombic efficiency. The superior performance is ascribed to (i) the high catalytic activity of LNCO towards oxygen reduction/evolution reactions; (ii) the increased temperature enabling fast kinetics; and (iii) the LiNO3-KNO3 molten salt enhancing the stability of the LOB operating at high temperature.

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

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

Hierarchically Porous and Minimally Stacked Graphene Cathodes for High‐Performance Lithium–Oxygen Batteries (Adv. Energy Mater. 2/2024)

Hierarchically Porous and Minimally Stacked Graphene Cathodes for High‐Performance Lithium–Oxygen Batteries (Adv. Energy Mater. 2/2024)

Co-deposition of conductive additives and lithium peroxide during discharge to boost the performance of lithium–oxygen batteries

A new method of utilizing carbon nanotubes as the electrolyte additive for lithium–oxygen batteries has been designed to overcome the shortcomings due to insulating discharge products.

Singlet oxygen is not the main source of electrolyte degradation in lithium oxygen batteries

The lithium-air (oxygen) battery could offer significant improvements in gravimetric energy density compared to lithium-ion technology. A major barrier to realising this goal is the oxidative degradation of the electrolyte...

Study of restricted diffusion of lithium salts in diglyme confined in mesoporous carbons as a model for cathodes in lithium-air batteries.

The Li+ ion mobility through the porous cathode is a critical aspect in the development of commercial Li-air batteries. The bulk transport properties of lithium salts in organic solvents are not reliable parameters for the design of this type of battery since confinement could significantly modify the transport properties, especially when pore diameters are below 10 nm. In this work, we studied the effect of the carbon mesostructure and surface charge on the diffusion of LiTf and LiTFSI salts dissolved in diglyme, typical electrolytes for lithium-air batteries. Interdiffusion coefficients of the salts were determined using a conductimetric method. NMR spectroscopy and relaxometry were used to explore the effect of the carbon structure and the surface charge density on the interaction between the electrolytes and the pore wall. We showed that carbon micro/mesoporous structure plays a critical role in the transport properties of the electrolyte, producing a decrease of up to 2-3 orders of magnitude in the salt interdiffusion coefficients when going from bulk solutions to pores below 4 nm in diameter. It was observed that for pores 25 nm in diameter, the reduction in the diffusion coefficient can be mainly ascribed to the porosity of the sample, giving tortuosity factors around 1. However, for smaller pore sizes (1-10 nm diameter) bigger tortuosity coefficients were observed and were related to strong ion-pore wall interactions. Moreover, it was noticed that the ratio between the diffusion coefficients of the two studied salts dissolved in diglyme, is different in bulk and under confinement, demonstrating that the interactions of the ions with the charged pore wall probably compete with the cation-anion interactions, affecting salt association under confinement.

The effect of electrolyte with binary solvents on improving the performance of rechargeable lithium–oxygen batteries

A bi-solvent electrolyte (G3/DMSO) was explored as a critical component to improve LOB performance from the perspective of electrolyte selection were rationally discussed. Cell capacity, coulombic efficiency and cycle life were all improved.

Piperidine-based ionic liquid additive with electrostatic shielding and redox activity enabling advanced lithium-oxygen batteries.

Here, we propose a piperidine-based ionic liquid additive. The electrostatic shielding effect of the piperidine cation (PP13+) effectively inhibits the growth of lithium dendrites. Simultaneously, the redox activity of the bromine anion synergistically reduces the overpotential. This approach significantly improves the cycling performance of lithium-oxygen batteries.

Spiers Memorial Lecture: Lithium air batteries - tracking function and failure.

The lithium-air battery (LAB) is arguably the battery with the highest energy density, but also a battery with significant challenges to be overcome before it can be used commercially in practical devices. Here, we discuss experimental approaches developed by some of the authors to understand the function and failure of lithium-oxygen batteries. For example, experiments in which nuclear magnetic resonance (NMR) spectroscopy was used to quantify dissolved oxygen concentrations and diffusivity are described. 17O magic angle spinning (MAS) NMR spectra of electrodes extracted from batteries at different states of charge (SOC) allowed the electrolyte decomposition products at each stage to be determined. For instance, the formation of Li2CO3 and LiOH in a dimethoxyethane (DME) solvent and their subsequent removal on charging was followed. Redox mediators have been used to chemically reduce oxygen or to chemically oxidise Li2O2 in order to prevent electrode clogging by insulating compounds, which leads to lower capacities and rapid degradation; the studies of these mediators represent an area where NMR and electron paramagnetic resonance (EPR) studies could play a role in unravelling reaction mechanisms. Finally, recently developed coupled in situ NMR and electrochemical impedance spectroscopy (EIS) are used to characterise the charge transport mechanism in lithium symmetric cells and to distinguish between electronic and ionic transport, demonstrating the formation of transient (soft) shorts in common lithium-oxygen electrolytes. More stable solid electrolyte interphases are formed under an oxygen atmosphere, which helps stabilise the lithium anode on cycling.

Nature of Li2O2 and its relationship to the mechanisms of discharge/charge reactions of lithium-oxygen batteries.

Lithium-air batteries (LABs) are considered one of the most promising energy storage devices because of their large theoretical energy density. However, low cyclability caused by battery degradation prevents its practical use. Thus, to realize practical LABs, it is essential to improve cyclability significantly by understanding how the degradation processes proceed. Here, we used online mass spectrometry for real-time monitoring of gaseous products generated during charging of lithium-oxygen batteries (LOBs), which was operated with pure oxygen not air, with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) tetraethylene glycol dimethyl ether (TEGDME) electrolyte solution. Linear voltage sweep (LVS) and voltage step modes were employed for charge instead of constant current charge so that the energetics of the product formation during the charge process can be understood more quantitatively. The presence of two distinctly different types of Li2O2, one being decomposed in a wide range of relatively low cell voltages (2.8-4.16 V) (l-Li2O2) and the other being decomposed at higher cell voltages than ca. 4.16 V (h-Li2O2), was confirmed by both LVS and step experiments. H2O generation started when the O2 generation rate reached a first maximum and CO2 generation took place accompanied by the decomposition of h-Li2O2. Based on the above results and the effects of discharge time and the use of isotope oxygen during discharge on product distribution during charge, the generation mechanism of O2, H2O, and CO2 during charging is discussed in relation to the reactions during discharge.

Enhancement of catalytic centres by RuO2 addition to CuFe2O4 cathode catalyst for rechargeable lithium–air batteries: influence of CO2 on Li–O2 battery performances

Herein, the oxygen reduction reaction and oxygen evolution reaction (ORR/OER) kinetics of the inverse-spinel CuFe2O4 catalyst was enhanced via the addition of a very low quantity of RuO2, which powers an LED when used in Li–air and Li–CO2 batteries.