Li-air Research Articles

A Quantitative Understanding of Electron and Mass Transport Coupling in Lithium–Oxygen Batteries

AbstractThe lithium–oxygen battery has the highest theoretical specific energy among all battery systems, while the actual value falls significantly short. The hindered oxygen and/or electron transport result(s) in limited utilization of the porous air electrode, while achieving a quantitative understanding of the electrochemistry and mass transport coupling is challenging. Herein, a porous electrode with highly consistent and controllable channel units is pioneered that excludes the randomness of disordered pores and consequently enables the investigation of control mechanisms. A three‐dimensional dynamic heterogeneous model is developed, providing the first spatio‐temporal distribution of LiO2 and revealing its reversed diffusion trajectories at limited electron transport. The synergistic combination of experiments and models identifies the crucial role of channel sizes on mechanisms that are divided into mass, hybridization, and electron transport control. For macropores, improving Li2O2 conductivity and mitigating solid‐liquid interface damage are urgent compared to enhancing oxygen diffusion. The unit model offers a promising approach to quantitatively understand the reaction and transport mechanisms in other battery systems with porous electrodes. This work represents a break through in knowledge of control mechanisms and guides the design of disordered electrodes for high‐performance lithium–oxygen batteries.

Study on evolution process and electrochemical behavior of porous cathode in discharge process of the solid-state lithium-oxygen battery

Solid-state lithium‑oxygen battery is one of the lithium-metal batteries with high theoretical specific capacity and strong safety. In order to explore the evolution process and electrochemical behavior of the battery, a study of combination of simulation and experiment is conducted in this paper. Firstly, solid-state lithium‑oxygen batteries with quartz tubes as the battery shell are designed for the experiment. FTIR and Raman results show that the lithium peroxide is produced as discharge products and SEM images show the product is accumulated on the surface of carbon particles and bound the carbon particles into blocks during the cathode evolution process. Then, a 1D multi-physics coupling field model referred to the experiment is established to investigate the electrochemical behavior of the battery. The calculated discharge curves are compared with the experimental discharge curves to verify the accuracy of the model. Using the model, the electrochemical behaviors, such as discharge product volume fraction, active three-phase interface, LATP phase potential and carbon phase potential, are analyzed. At last, the reasons for discharge termination are attributed to the accumulation of lithium peroxide and the decline of active three-phase interface.

Probing interfacial electrochemistry by in situ atomic force microscope for battery characterization

AbstractLithium‐ion batteries (LIBs) have been widely used in electric vehicles and energy storage industries. An understanding of the reaction processes and degradation mechanism in LIBs is crucial for optimizing their performance. In situ atomic force microscopy (AFM) as a surface‐sensitive tool has been applied in the real‐time monitoring of the interfacial processes within lithium batteries. Here, we reviewed the recent progress of the application of in situ AFM for battery characterizations, including LIBs, lithium–sulfur batteries, and lithium–oxygen batteries. We summarized advances in the in situ AFM for recording electrode/electrolyte interface, mechanical properties, morphological changes, and surface evolution. Future directions of in situ AFM for the development of lithium batteries were also discussed in this review.

The initial stages of Li2O2 formation during oxygen reduction reaction in Li-O2 batteries: The significance of Li2O2 in charge-transfer reactions within devices

Lithium-oxygen batteries are a promising technology because they can greatly surpass the energy density of lithium-ion batteries. However, this theoretical characteristic has not yet been converted into a real device with high cyclability. Problems with air contamination, metallic lithium reactivity, and complex discharge and charge reactions are the main issues for this technology. A fast and reversible oxygen reduction reaction (ORR) is crucial for good performance of secondary batteries’, but the partial knowledge of its mechanisms, especially when devices are concerned, hinders further development. From this perspective, the present work uses operando Raman experiments and electrochemical impedance spectroscopy (EIS) to assess the first stages of the discharge processes in porous carbon electrodes, following their changes cycle by cycle at initial operation. A growth kinetic formation of the discharge product signal (Li2O2) was observed with operando Raman, indicating a first-order reaction and enabling an analysis by a microkinetic model. The solution mechanism in the evaluated system was ascribed for an equivalent circuit with three time constants. While the time constant for the anode interface reveals to remain relatively constant after the first discharge, its surface seemed to be more non-uniform. The model indicated that the reaction occurs at the Li2O2 surface, decreasing the associated resistance during the initial discharge phase. Furthermore, the growth of Li2O2 forms a hetero-phase between Li2O2/electrolyte, while creating a more compact and homogeneous on the Li2O2/cathode surface. The methodology here described thus offers a way of directly probing changes in surface chemistry evolution during cycling from a device through EIS analysis.

Rechargeable Lithium-Air Batteries with Practically High Energy Density

Rechargeable Lithium-Air Batteries with Practically High Energy Density

Heme-Based Composites as Cathode Catalysts for Lithium-Oxygen Batteries and Analysis of the Reaction Mechanism

Despite the high theoretical energy density of lithium-oxygen (Li-O2) batteries, the charge/discharge efficiency is unsatisfactory. To overcome this critical problem, we synthesized heme-graphene composites (HEME-GO) as catalysts for Li-O2 batteries. The introduction of graphene produced π-π interactions with the heme matrix, resulting in a composite with enhanced ORR/OER catalytic activity. The free energy diagram of the redox reaction was calculated using density functional theory (DFT) for HEME-GO based on the four-electron reaction pathway, and it was demonstrated that HEME-GO has the lowest ORR overpotential (0.67 V) and OER overpotential (0.53 V). The catalytic mechanism of HEME-GO was also quantitatively described by calculating the adsorption energy of intermediates in the rate determining step (RDS). In addition, the Li-O2 batteries with the composite catalyst exhibited better cycling performance, discharge capacity (7770 mAh g−1), and lower overpotential due to the ability of heme to scavenge superoxide radicals and thus protect the electrode. The results in this paper contribute to the understanding of the redox process of Li-O2 batteries for organic systems and suggest innovative ideas for the design of environmentally friendly batteries.

Tunable Oxygen Vacancies of Cobalt Oxides in Lithium-Oxygen Batteries: Morphology Control of Discharge Product.

The discharge product Li2O2 is difficult to decompose in lithium-oxygen batteries, resulting in poor reversibility and cycling stability of the battery, and the morphology of Li2O2 has a great influence on its decomposition during the charging process. Therefore, reasonable design of the catalyst structure to improve the density of catalyst active sites and make Li2O2 form a morphology which is easy to decompose in the charging process will help improve the performance of battery. Here, we demonstrate a series of hollow nanoboxes stacked by Co3O4 nanoparticles with different sizes. The results show that the surface of the nanoboxes composed of smaller size Co3O4 nanoparticles contains abundant pore structure and higher concentration of oxygen vacancies, which changes the adsorption energy of reactants and intermediates, providing more nucleation sites for Li2O2, thereby forming Li2O2 with high dispersion, which is easier to decompose during charging, and eventually improve the performance of the battery. This provides an important idea for the structural design of the cathode catalyst in lithium-oxygen batteries and the regulation of Li2O2 morphology.

B-N Co-Doped Biphenylene as a Metal-Free Cathode Catalyst for Li-O2 Batteries: a Computational Study.

Lithium-oxygen batteries (LOBs) meet the growing demand for long-distance transportation over electric vehicles but face challenges because of the lack of high-performance cathode catalysts. Herein, using density functional theory calculations, we report a unique graphene allotrope, biphenylene, of which the doping structures exhibit great potential as metal-free catalysts for LOBs. Our modeling results demonstrate that the biphenylene nanosheets retain metallic properties after B doping, N doping, or B-N co-doping. Compared with the pristine biphenylene, the catalytic activity of the doped biphenylene is greatly improved due to charge redistributions. Notably, the overpotentials of the B-N co-doped biphenylene are as low as 0.19 and 0.18 V for the discharge and charge processes, respectively. Based on the electronic structure and bonding analysis, we identify two factors, i. e., Li-O bond strength and *Li2 O2 adsorption energy, that can influence the Li-O2 electrochemical reactions. This study not only proposes a promising cathode catalyst but also provides insights into optimizing cathode catalysts for LOBs.

Changes in double layer capacitance of the positive electrode in Li-O2 battery during discharge: Effect of active material and aprotic electrolyte solvent

Changes in the double-layer capacitance of a positive electrode (CDL) are investigated during the discharge of a lithium-oxygen battery (LOB) having various carbon materials (CM), including XC-72, Super P, EC-300 J, and CNT, and electrolytes based on tetraglyme and DMSO, containing 0.1 M LiClO4. It is shown that the initial value of CDL increases proportionally to the external surface area of the carbon material in both the tetraglyme- and DMSO-based electrolyte. The difference between the CDL values in these electrolytes can be explained by the different wetting abilities of the solvents, as well as the ability of the DMSO medium to dissolve the binder (PVDF). During the LOB discharge, a decrease in CDL is observed, which is associated with increasing passivation of the positive electrode with lithium peroxide (Li2O2)). The highest (Li2O2) value (0.5–0.7) is observed for XC-72 and EC-300 J carbon black having the lowest average pore size (9 and 8 nm, respectively) among the studied materials. Nonetheless, no pronounced dependence of (Li2O2) on the nature of a solvent was observed under identical measurement conditions. Along with blocking the surface with lithium peroxide, oxygen transport limitations have a significant impact on the discharge process, which is most pronounced for large-pore CMs (Super P and CNT). Even at a relatively low (Li2O2) (from 0.15 to 0.24), the voltage of such LOBs decreases to 2 V. The results demonstrate that the initial parameter CDL of the active material can be used as a new criterion for pre-selection the electrolyte for LOB.

Typology of Battery Cells - From Liquid to Solid Electrolytes.

The field of battery research is bustling with activity and the plethora of names for batteries that present new cell concepts is indicative of this. Most names have grown historically, each indicative of the research focus in their own time, e.g. lithium-ion batteries, lithium-air batteries, solid-state batteries. Nevertheless, all batteries are essentially made of two electrode layers and an electrolyte layer. This lends itself to a systematic and comprehensive approach by which to identify the cell type and chemistry at a glance. The recent increase in hybridized cell concepts potentially opens a world of new battery types. To retain an overview of this dynamic research field, each battery type is briefly discussed and a systematic typology of battery cells is proposed in the form of the short and universal cell naming system AAM XEBCAM (AAM: anode active material; X: L (liquid), G (gel), PP (plasticized polymer), DP (dry polymer), S (solid), H (hybrid); EB: electrolyte battery; CAM: cathode active material). This classification is based on the principal ion conduction mechanism of the electrolyte during cell operation. Even though the presented typology initiates from the research fields of lithium-ion, solid-state and hybrid battery concepts, it is applicable to any battery cell chemistry.

Enhancing the Performance of Lithium-Oxygen Batteries with Quasi-Solid Polymer Electrolytes.

The quasi-solid electrolyte membranes (QSEs) are obtained by solidifying the precursor of unsaturated polyester and liquid electrolyte in a glass fiber. By modifying the ratio of tetraethylene glycol dimethyl ether, QSE with balanced ionic conductivity, flexibility, and electrochemical stability window is acquired, which is helpful for inhibiting the decomposition of electrolyte on the cathode surface. The QSE is beneficial to the interfacial reaction of Li+, electrons, and O2 in the quasi-solid lithium-oxygen battery (LOB), can reduce the crossover of oxygen to the anode, and extend the cycle life of LOBs to 317 cycles. Benefitting from the application of QSE, a more stable solid electrolyte interface layer can be constructed on the anode side, which can homogenize Li+ flux and facilitate uniform Li deposition. Lithium-oxygen pouch cell with in situ formed QSE2 works well when the cell is folded or a corner is cut off. Our results indicate that the QSE plays important roles in both the cathode and Li metal anode, which can be further improved with the in situ forming strategy.

Intrinsic Stress-strain in Barium Titanate Piezocatalysts Enabling Lithium-Oxygen Batteries with Low Overpotential and Long Life.

Rechargeable lithium-oxygen (Li-O2 ) batteries with high theoretical energy density are considered as promising candidates for portable electronic devices and electric vehicles, whereas their commercial application is hindered due to poor cyclic stability caused by the sluggish kinetics and cathode passivation. Herein, the intrinsic stress originated from the growth and decomposition of the discharge product (lithium peroxide, Li2 O2 ) is employed as a microscopic pressure resource to induce the built-in electric field, further improving the reaction kinetics and interfacial Lithium ion (Li+ ) transport during cycling. Piezopotential caused by the intrinsic stress-strain of solid Li2 O2 is capable of providing the driving force for the separation and transport of carriers, enhancing the Li+ transfer, and thus improving the redox reaction kinetics of Li-O2 batteries. Combined with a variety of in situ characterizations, the catalytic mechanism of barium titanate (BTO), a typical piezoelectric material, was systematically investigated, and the effect of stress-strain transformation on the electrochemical reaction kinetics and Li+ interface transport for the Li-O2 batteries is clearly established. The findings provide deep insight into the surface coupling strategy between intrinsic stress and electric fields to regulate the electrochemical reaction kinetics behavior and enhance the interfacial Li+ transport for battery system.

Preparation of Composite Single‐Ion Conductor Membrane and Its Application in Lithium–Oxygen Battery

Redox mediators (RMs) are reported to effectually encourage the inactive decomposition of discharge products in lithium–oxygen batteries (LOBs); however, oxidized RMs and other injurious species still attack the Li anodes. An ionic liquid (IL)‐modified PVDF single‐lithium‐ion conducting composite membrane that can permit Li+ only but blocks anions and other molecules is prepared. The PVDF is combined with the strong‐acid cation styrene exchange resin with cation exchange characteristics to make a heterogeneous composite single‐ionic conductor membrane and the IL modification causes the formation of a more‐dense groove inside the PVDF membrane apparently strengthening the conductivity of the membrane without losing its impermeability to cations and discharge intermediates. The utility of the modified composite PVDF (MCP) separator greatly extends the cycle life of the LOB from 66 to 347 cycles at 1000 mAg−1 and 1000 mAhg−1 compared to cells using glass fiber separators. Rate performance is significantly enhanced at 3000 and 5000 mAg−1, increasing from 33 and 21 cycles to 171 and 137 cycles. The full discharge capacity also expands from 3702 to 51 205 mAhg−1. The MCP separator enables iodide‐assisted cathode processes and improves lithium anode stripping/plating, which is essential to improve the performance of nonelectrolytic LOBs.

Anion exchange strategies in radical doped hole transporting material for high-efficiency perovskite solar cells

Perovskite solar cells (PSCs) have received significant attention due to their superior photovoltaic conversion capability. To date, most efficient PSCs use p-doped organic semiconductors as hole-transporting layers (HTL). Many evidences show that the generally used p-doping system, i.e. lithium bis(trifluoromethane)sulfonimide and air exposure threaten the reproducibility and stability of PSCs. Recently, free radicals doped HTL have been used to fabricate efficient PSCs without using anying harmful dopants. Herein, we found that the low doping efficiency of radials is due to a weak Madelung potential. We developed a spontaneous anion exchange to stabilize the radical doped HTL via introducing an additional anion into the host-guest system. Conductivity and interfacial charge transfer are significantly enhanced by regulating the size of anions. We found that the conductivity and device performance is increased when the size of the anion increases. As a result, a champion efficiency of 20.7% under AM 1.5G 1-sun irradiation is achieved, which is comparable with the conventionally doped HTL. Moreover, the solar cells showed significantly enhanced stability against the humidity stress, which we attribute to the use of HTLs devoid of environmental sensitive additives.

ZIF-67 derived 3D nanocage-shaped FeCoNi layered double hydroxides as an electrocatalyst for improving the performance of LOBs

Layered double hydroxides (LDHs) with unique structure features are regarded as ideal materials for energy storage. Developing highly efficient cathode catalysts is crucial for improving the storage capacity and stability of lithium-oxygen batteries (LOBs). Herein, we proposed a facile solvothermal strategy to prepare different metal molar ratios of trimetallic FeCoNi LDHs using the zeolitic imidazolate framework-67 (ZIF-67) as a template. When the metal molar ratios of Fe/Ni = 1.7, the obtained FeCoNi LDH (FCN-C) exhibits a 3D nanocage-shaped structure with highly ordered flower-like nanosheets on the surface. The well-designed structures exhibit high specific surface areas and abundant mic-mesoporous channels, which are favored for the transport of electrons and ions diffusion. The synergistic effects of FeCoNi LDH components can effectively regulate the electronic structure and deliver striking electrochemical activities. Specifically, the LOBs with FCN-C cathode possess an excellent specific capacity of 17598.5 mAh g−1 at 0.05 mA cm−2. Under 0.05 mA cm−2 with a cutoff capacity of 500 mAh g−1, the LOBs assembled by FCN-C cathode can achieve 213 cycles, and it is much longer than that of other FeCoNi LDHs cathodes. This simple preparation method can provide new insight to design efficient electrocatalysts for energy applications.

Enhancing lithium-air battery performance through CoPc@CNT composites: Electrochemical analysis and insights

Cobalt-phthalocyanine (CoPc) catalysts have shown great promise for enhancing the performance of lithium‑oxygen (Li-O2) batteries, offering benefits such as efficient lithium storage, high reversible capacity, improved cycle performance, and enhanced charge and discharge capacity. In this study, we focused on the synthesis of CoPc‑carbon nanotube (CNT) composites with porous structure. The composites were prepared by synthesizing CoPc compounds and interacting them with CNTs using a 3D ball mill shaker. Comprehensive spectroscopic techniques including NMR, FTIR, and UV were employed to characterize the newly synthesized phthalonitrile and phthalocyanine compounds. The surface morphologies of the composite materials were investigated using SEM, EDX, mapping and TEM analysis, enabling the determination of particle sizes and chemical compositions. XRD and XPS analyses confirmed that the composite structures were consistent with the existing literature. BET analysis revealed multilayer isotherm for the composites, indicating their favorable properties. The composite catalysts were incorporated into batteries and their performance was evaluated through various electrochemical tests. Notably, the CoPc1-CNT composite exhibited a remarkable discharge capacity of 3400 mAh g−1catalyst in the prepared battery.

Optimizing d-orbital occupation on interfacial transition metal sites via heterogeneous interface engineering to accelerate oxygen electrode reaction kinetics in lithium-oxygen batteries

Aprotic lithium-oxygen batteries (LOBs) possess extremely high theoretical energy density of about 3500 Wh kg-1, which is superior to state-of-the-art lithium-ion batteries. However, the poor energy efficiency and cyclability originated from sluggish kinetics of oxygen electrode reactions in LOBs severely restrict their development and practical application. The solution to these challenges is closely related to the construction of electrocatalysts with both high catalytic activity and stability for oxygen redox reactions in LOBs. In this work, Co3O4 @NiFe2O4 composite with modified heterogeneous interface is fabricated and studied as oxygen electrode catalyst for LOBs. It is theoretically predicted that the electron transfer at the heterogeneous interface in Co3O4 @NiFe2O4 is capable of reducing the occupation of eg electrons in the interfacial Ni sites, leading to the rearrangement of electrons with enhanced spin polarization in the d orbital and the upshift of the d-band center toward Fermi level, eventually enabling the smooth electron transfer between Co3O4 @NiFe2O4 and oxygenated species due to the facile formation of Ni-O bond. This endows Co3O4 @NiFe2O4 based LOBs with high specific capacity of 12697 mAh g-1 and extremely low overpotential of 0.68 V at 100 mA g-1, as well as long cycle life of 274 times at a high current density of 500 mA g-1. This work provides a new strategy for adjusting the surface electronic structure of oxygen electrode catalysts to accelerate oxygen redox kinetics in LOBs.

Superior lithium dendrite suppression and air stability of dual Sc and O substituted Li-argyrodites and their enhanced cyclability in Li-batteries

Sulfide solid electrolyte has recently come to be considered a suitable electrolyte for lithium batteries because of its high ionic conductivity. However, it cannot be implemented in real time applications because of lithium dendrites and moisture sensitive issues. In this work, we solve the aforementioned issues through Sc2O3 substitution on P and S-site in Li6PS5Cl structure. The prepared Sc2O3 substituted Li6PS5Cl shows an ionic conductivity values of 3.80 mS cm−1, which is somewhat lower compared to Li6PS5Cl (4.91 mS cm−1). Notably, after Sc2O3 substitution in Li6PS5Cl that boost up the interface stability with lithium. Moreover, it exhibits an excellent critical current density of 0.6 mA cm−2 than bare electrolyte (0.2 mA cm−2). Also, it shows the better DC cyclability at 0.2 and 0.3 mA cm−2 without internal short circuit after 200 cycles. Atmospheric stability analysis assures that the optimized electrolyte shows high tolerance against dry air. Finally, we assembled the battery that shows the discharge capacity of 183.3 mAh g−1, and the capacity is found to be retained over 94.5 % after 180 cycles. Importantly, the battery demonstrates a good discharge capacity of 139.9 mAh g−1 at 1C rate.

A Novel Approach for Development of Stable Quasi‐Solid Lithium‐O2 Batteries: Assembly and Performances of Double Layer Gel Polymer Electrolytes

AbstractGel‐polymer electrolytes (GPEs) offer a suitable alternative to flammable organic liquid electrolytes in lithium‐oxygen batteries (LOBs) to address safety concerns. However, a major challenge with GPEs is their low ionic conductivity. To enhance the ionic conductivity of GPEs, active inorganic particles have been incorporated. To increase the ionic conductivity of GPE, active inorganic particles have been reinforced in GPE. While this increases the ionic conductivity, it also leads to blockage of the cathode porous structure and reduces the actual surface area of the cathode materials, resulting in poor battery performance. This study proposes a novel double‐layer polymer gel electrolyte (d‐GPE) that exhibits both high ionic conductivity and stability for quasi solid‐state LOBs. The double‐layer GPE consists of a bare GPE layer integrated in the cathode, and a composite GPE (c‐GPE, containing 5 wt. % lithium aluminum titanium phosphate (LATP)), which is in contact with Li anode and bare‐GPE. The produced double‐layer gel polymer electrolyte displays high reaction kinetic and better stability due to the excellent electrode/electrolyte interface and rapid oxygen diffusion in the air‐cathode. Furthermore, the d‐GPE electrolyte is resistant to fire and protects Li from dendrite growth and water molecules attack, indicating tremendous promise for the development of practical LOBs.

Investigating the Role of an Anionic Surfactant in Optimizing Lithium–Air Batteries Based on Dissipative Particle Dynamics and Electrochemical Experiments

Investigating the Role of an Anionic Surfactant in Optimizing Lithium–Air Batteries Based on Dissipative Particle Dynamics and Electrochemical Experiments