Iterative Machine Learning-Guided Discovery of Transition Metal Compounds as Catalysts for Li-CO2 and Li-Air Batteries.

Global warming and climate change are urgent international issues, mainly stemming from the overreliance on fossil fuels. To combat this, researchers are actively striving for carbon neutrality [1]. Energy storage devices are crucial in advancing future renewable energy systems. Commercial Li-ion batteries, utilizing a LiCoO2 cathode and a carbon anode, offer a specific energy density limited to 387 Wh kg-1. Li-air batteries have emerged as promising energy storage solutions, boasting impressive energy densities of 1910 Wh kg-1 and 3460 Wh kg-1 with liquid and solid electrolytes, respectively [2-3].In 2011, Takechi et al. reported the first functional Li-O2/CO2 battery prototype [4], revealing that employing CO2 as a working gas enhances discharge capacity compared to Li-O2 batteries. Consequently, several studies have focused on the electrochemical performance of Li-CO2 batteries. Despite their impressive discharge capacity, these batteries grapple with challenges such as limited cycle life, heightened volatility of electrolytes, and sluggish reaction kinetics. Therefore, understanding the electrochemical reactions in Li-CO2 batteries and their degradation mechanisms during cycling is essential. In addition, selecting the optimal electrode-electrolyte configurations in Li-CO2 batteries is equally vital to address any safety concerns that have arisen to date.Using a simple solution-based method, this study synthesized a solid electrolyte, Li1.4Al0.4Ge0.1Ti1.5(PO4)3 (LAGTP). Stoichiometric amounts of LiCl (98.2%, SAMCHUN), Al(NO3)3∙9H2O (98%, SAMCHUN), GeO2 (99.9%, ALDRICH), C16H36O4Ti (97%, SAMCHUN), and NH4H2(PO4)3 (98%, SAMCHUN) were thoroughly mixed in deionized (DI) water. The solution was stirred magnetically and then ball-milled (Pulverisette 5, Fritsch) for 2 h. Subsequently, the solution was dried at 80 °C for 12 h to remove the solvent. It was then ground into a fine powder and calcined at 800 °C for 12 h. This heat treatment helped complete the chemical reaction and release volatile impurities to form pure LAGTP powder. Following heat treatment, the powder was mixed with 2 wt.% polyvinyl alcohol (PVA) binder and compressed into circular pellets with diameters of 15 mm. Finally, the pellets were sintered at 900 °C for 4 h in air to reduce porosity and increase relative density. LAGTP exhibited outstanding ionic conductivity (1.05 × 10-3 S cm-1) and a low activation energy (0.237 eV).The LAGTP pellet was utilized as a solid-state electrolyte in a Li-CO2 battery, demonstrating charge-discharge characteristics through a reversible electrochemical reaction (4Li+ + 3CO2 ↔ 2Li2CO3 + C). Multi-walled carbon nanotubes, drop-cast on carbon cloth, served as the cathode material. The Li-CO2 mesh-type coin cell assembly comprised a Li anode, an MWCNT drop-cast carbon cloth cathode, and a LAGTP solid electrolyte. Initially, the cathode was prepared by mixing MWCNTs (>98%, 12 nm diameter, seven layers), polypyrrole, and polyvinylidene fluoride (PVDF) in a 7:2:1 weight ratio in an N-methyl-2-pyrrolidone (NMP) solvent. For electrochemical characterization, a Swagelok-type Li-CO2 test kit was assembled in a glove box filled with Ar, maintaining H2O and O2 levels below 1 ppm. Finally, the current density and capacity were normalized to the weight of the MWCNTs on the carbon-cloth cathode. The battery underwent 60 cycles with a cut-off capacity of 1000 mAh g-1 at various current densities, and a comprehensive charge and discharge test was performed at 100 mA g-1. Throughout the charge/discharge process, the particle size of inactive lithium increased on the cathode surface, obstructing active sites for conversion. Post-cycling analyses were conducted to elucidate the cathode degradation mechanism. The integration of LAGTP substantially improved battery cycle life and safety, positioning it as a viable option for next-generation, high-performance Li-CO2 batteries.

Research progress of cathode catalyst for field-assisted Li-O2/CO2 battery

At present, photoassisted Li-air batteries are considered to be an effective approach to overcome the sluggish reaction kinetics of the Li-air batteries. And, the organic liquid electrolyte is generally adopted by the current conventional photoassisted Li-air batteries. However, the superior catalytic activity of photoassisted cathode would in turn fasten the degradation of the organic liquid electrolyte, leading to limited battery cycling life. Herein, we tame the above limitation of the traditional liquid electrolyte system for Li-CO2 batteries by constructing a photoassisted all-solid-state Li-CO2 battery with an integrated bilayer Au@TiO2/Li1.5Al0.5Ge1.5(PO4)3 (LAGP)/LAGP (ATLL) framework, which can essentially improve battery stability. Taking advantage of photoelectric and photothermal effects, the Au@TiO2/LAGP layer enables the acceleration of the slow kinetics of the carbon dioxide reduction reaction and evolution reaction processes. The LAGP layer could resolve the problem of liquid electrolyte decomposition under illumination. The integrated double-layer LAGP framework endows the direct transportation of heat and Li+ in the entire system. The photoassisted all-solid-state Li-CO2 battery achieves an ultralow polarization of 0.25 V with illumination, as well as a high round-trip efficiency of 92.4%. Even at an extremely low temperature of -73 °C, the battery can still deliver a small polarization of 0.6 V by converting solar energy into heat to achieve self-heating. This study is not limited to the Li-air batteries but can also be applied to other battery systems, constituting a significant step toward the practical application of all-solid-state photoassisted Li-air batteries.

Metal-air batteries, especially Li-air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO2 (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li2 CO3 , making the battery less rechargeable. To make the Li-CO2 batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO2 reduction and evolution reactions and investigate the electrochemical behavior of Li-CO2 batteries. Here, we demonstrate a rechargeable Li-CO2 battery with a high reversibility by using B,N-codoped holey graphene as a highly efficient catalyst for CO2 reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as-prepared Li-CO2 batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long-term cycling stability over 200 cycles at a high current density of 1.0 A g-1 . Our results open up new possibilities for the development of long-term Li-air batteries reusable under ambient conditions, and the utilization and storage of CO2 .

Activity evaluation and reaction mechanisms of highly efficient dual-atom transition metal catalysts in Li-CO2 batteries

As a main reason of greenhouse effect, CO2 emission should be reduced to alleviate further environmental pollution such as global warming and climate changes.[1] Considering wide and substantial utilization of fossil fuels in various industries, it is hard to diminish the emission in a short time. To handle the problems, carbon capture and storage (CCS) technologies have emerged as new breakthrough of relieving the amount of CO2 in atmosphere, fixing and storing the gaseous CO2 to solid phases.[2] Li-CO2 batteries as electrochemical CCS technology have been spotlighted for their bi-functional applications enabling both energy storage system and environment-friendly CO2 fixation.[3] The Li-CO2 batteries operate with CO2 (Mw. CO2: 44) as a cathode material, which is two-fold lighter than transition metal (e.g. Mw. LiCoO2: 98) in Li-ion batteries, indicating distinguished energy potentials. However, insulating discharge products and inactive reactions of the Li-CO2 cells during cycling lead to cell degradation, showing poor cyclability and low efficiency. Therefore, to utilize the Li-CO2 batteries as next-generation energy storage system, various catalysts should be introduced, facilitating the discharge/charge reaction.In both economic and eco-friendly respects, using bio-waste as a precursor has attracted the attention in the field of catalyst development.[4] Hemoglobin obtained from blood-wastes (such as slaughter and medical wastes) has been introduced as a cathode catalyst.[5-6] It is composed of four globular protein chains each with a Fe-centered porphyrin called heme, which is capable of changing their oxidation numbers. With redox reactions of centered iron, hemoglobin can bind with CO2, interacting directly with the cell reaction in Li-CO2 batteries. Furthermore, various cation (e.g. iron) and anion (e.g. oxygen, nitrogen, and carbon) resources in hemoglobin can be employed as catalytic components. Diverse treatments and procedures can be performed to maximize catalytic effects of hemoglobin-derived catalyst.In this presentation, we introduce a new method, applying capillary action of hemoglobin precursor into CNT, to fabricate Fe nanoparticles embedded in N-doped CNT (Fe NPs@N-CNT) catalysts. By simple treatments, we successfully synthesized Fe NPs@N-CNT and examined the morphological and structural characteristics of the catalyst. The pore size of CNT provides strong force of capillary motion to draw the precursor solution into the tubes and subsequent segregation of Fe components are achieved, showing crystalline structure in TEM analysis. We performed the electrochemical cell tests, employing Fe NPs@N-CNT catalysts, and confirmed the catalytic activities of reduced charge overpotential and enhanced capacity in both discharge and charge process. The utilization of bio-waste as the catalysts provides environmental merits for developing eco-friendly Li-CO2 batteries and moreover, the novel application of capillary motion to fabricate Fe NPs@N-CNT catalysts offers new pathway to develop various catalytic materials.[1] A. M. Appel, J. E. Bercaw, A. B. Bocarsly, H. Dobbek, D. L. DuBois, M. Dupuis, J. G. Ferry, E. Fujita, R. Hille and P. J. Kenis, Chemical reviews, 2013, 113, 6621-6658.[2] N. MacDowell, N. Florin, A. Buchard, J. Hallett, A. Galindo, G. Jackson, C. S. Adjiman, C. K. Williams, N. Shah and P. Fennell, Energy & Environmental Science, 2010, 3, 1645-1669.[3] Y. Qiao, J. Yi, S. C. Wu, Y. Liu, S. X. Yang, P. He and H. S. Zhou, Joule, 2017, 1, 359-370.[4] Z. Ma, K. Wang, Y. Qiu, X. Liu, C. Cao, Y. Feng and P. Hu, Energy, 2018, 143, 43-55.[5] W.-H. Ryu, F. S. Gittleson, J. M. Thomsen, J. Li, M. J. Schwab, G. W. Brudvig and A. D. Taylor, Nature communications, 2016, 7, 1-10.[6] J.-Y. Lee, H.-S. Kim, J.-S. Lee, C.-J. Park and W.-H. Ryu, ACS Sustainable Chemistry & Engineering, 2019, 7, 16151-16159.

The need for environmentally friendly and effective energy storage technologies is growing urgently in response to the rising energy demand and the seriousness of the environmental issues, in order to meet the Double Carbon objective. Li-CO2 batteries are a newer battery technology that has drawn a lot of interest. Its distinctiveness comes from the utilization of CO2 as a key component in energy storage, which can efficiently transform CO2 supplies into energy preservation and potentially be sustainable and environmentally friendly. This article examines the Li-CO2 battery's internal working mechanisms, delves into the selection and development of positive electrode catalysts, and contrasts several materials to list their benefits and drawbacks. Carbon-based materials, precious metals, and their compounds, and transition metals and their complexes are the main areas of emphasis. Carbon materials' exceptional conductivity, enormous specific surface area, and high commercial viability are underlined. The performances of precious metals and transition metals paired with carbon materials are compared in detail. Finally, suggestions for further research into potential cathode catalytic materials for Li-CO2 batteries are provided based on the effectiveness and practical utility of various materials. In an attempt to combat global warming and environmental pollution, new methods for converting waste gases, such as carbon dioxide, into energy will be developed thanks to research on Li-CO2 batteries. The features of this battery technology, such as its high density of energy and lengthy cycle life, are projected to make it more practical to store and use renewable energy.

As energy storage systems with great prospects, both Li-air and Li-CO2 batteries suffer from the low energy efficiency and poor cycle performance caused by the accumulation of Li2CO3 during cycling. Therefore, a complete electrochemical decomposition of Li2CO3 during charging will greatly improve the performance of Li-air and Li-CO2 batteries. However, our understanding of the electrochemical decomposition mechanism of Li2CO3 is very limited. In this work, we investigated the electrochemical reaction mechanism of Li2CO3 oxidation. During the charging process of Li2CO3 electrode, CO2 was detected as the main charging product while at the same time no gaseous O2 was released. With the help of isotopic tracing and GC-MS method, we were able to eliminate the possibility of the direct self-decomposition reaction of Li2CO3 as well as the reaction between Li2CO3 and carbon. Further experiments illustrated that superoxide radicals and dissolved oxygen generate during the charging process of Li2CO3 and will lead to electrolyte solvent decomposition. Combining the above results, we suggest that the decomposition mechanism of Li2CO3 can be described as follows: Li2CO3 decomposes into CO2, superoxide radicals and O2(formed by part of the superoxide radicals). The O2 and superoxide radicals are consumed by the further reaction with tetraglyme electrolyte solvent and thus fail to be detected.

Owing to the energy crisis and environmental pollution, developing efficient and robust electrochemical energy storage (or conversion) systems is urgently needed but still very challenging. Next-generation electrochemical energy storage and conversion devices, mainly including fuel cells, metal-air batteries, metal-sulfur batteries, and metal-ion batteries, have been viewed as promising candidates for future large-scale energy applications. All these systems are operated through one type of chemical conversion mechanism, which is currently limited by poor reaction kinetics. Single atom catalysts (SACs) perform maximum atom efficiency and well-defined active sites. They have been employed as electrode components to enhance the redox kinetics and adjust the interactions at the reaction interface, boosting device performance. In this Review, we briefly summarize the related background knowledge, motivation and working principle toward next-generation electrochemical energy storage (or conversion) devices, including fuel cells, Zn-air batteries, Al-air batteries, Li-air batteries, Li-CO2 batteries, Li-S batteries, and Na-S batteries. While pointing out the remaining challenges in each system, we clarify the importance of SACs to solve these development bottlenecks. Then, we further explore the working principle and current progress of SACs in various device systems. Finally, future opportunities and perspectives of SACs in next-generation electrochemical energy storage and conversion devices are discussed.

Lithium-carbon dioxide (Li-CO2) batteries provide an extremely feasible strategy for sustainable development and carbon neutrality. However, due to the sluggish kinetics and complex interfacial reactions, Li-CO2 batteries are limited by low output voltage and poor cycling stability. Developing efficient and durable catalysts remains an urgent challenge. Transition metal oxides have gained significant attention owing to their availability and stability for electrocatalytic reactions, but their catalytic activity remains unsatisfactory toward Li-CO2 batteries. Herein, this work proposes an asymmetric Fe/Cu-incorporated Co3O4 tactic system to tune charge distribution for motivating efficient electrocatalysis and decipher the mechanism of asymmetric structure modulation on the promotion of catalytic activity and stability. It is unraveled that d-orbital spin splitting induces the modification of nondegenerate state, which enhances catalyst durability, while simultaneously increasing electron occupancy in dxz / yz orbitals. This higher electron occupancy facilitates the hybridization with the p orbitals of reactants and intermediates via π bonding, thereby strengthening the adsorption activity. In consequence, the Li-CO2 battery with Cu-Co3O4 cathode demonstrates a low overpotential of 0.73V and high Coulombic efficiency of 96%, outperforming batteries with Co3O4 and Fe-Co3O4. This work offers a unique insight for electronic structure regulation strategy and displays a high-performance catalyst for Li-CO2 batteries.

Carbonate decomposition: Low-overpotential Li-CO2 battery based on interlayer-confined monodisperse catalyst

The rechargeable Li-CO2 battery has attracted considerable attention in recent years because of its carbon dioxide (CO2) utilization and because it represents a practical Li-air battery. As with other battery systems such as the Li-ion, Li-O2, and Li-S battery systems, understanding the reaction pathway is the first step to achieving high battery performance because the performance is strongly affected by reaction intermediates. Despite intensive efforts in this area, the effect of material parameters (e.g., the electrolyte, the cathode, and the catalyst) on the reaction pathway in Li-CO2 batteries is not yet fully understood. Here, we show for the first time that the discharge reaction pathway of a Li-CO2 battery composed of graphene nanoplatelets/beta phase of molybdenum carbide (GNPs/β-Mo2C) is strongly influenced by the dielectric constant of its electrolyte. Calculations using the continuum solvents model show that the energy of adsorption of oxalate (C2O42-) onto Mo2C under the low-dielectric electrolyte tetraethylene glycol dimethyl ether is lower than that under the high-dielectric electrolyte N,N-dimethylacetamide (DMA), indicating that the electrolyte plays a critical role in determining the reaction pathway. The experimental results show that under the high-dielectric DMA electrolyte, the formation of lithium carbonate (Li2CO3) as a discharge product is favorable because of the instability of the oxalate species, confirming that the dielectric properties of the electrolyte play an important role in the formation of the discharge product. The resulting Li-CO2 battery exhibits improved battery performance, including a reduced overpotential and a remarkable discharge capacity as high as 14,000 mA h g-1 because of its lower internal resistance. We believe that this work provides insights for the design of Li-CO2 batteries with enhanced performance for practical Li-air battery applications.

Machine learning (ML) workflows are extremely complex. The typical workflow consists of distinct stages of user interaction, such as preprocessing, training, and tuning, that are repeatedly executed by users but have heterogeneous computational requirements. This complexity makes it challenging for ML users to correctly provision and manage resources and, in practice, constitutes a significant burden that frequently causes over-provisioning and impairs user productivity. Serverless computing is a compelling model to address the resource management problem, in general, but there are numerous challenges to adopt it for existing ML frameworks due to significant restrictions on local resources. This work proposes Cirrus---an ML framework that automates the end-to-end management of datacenter resources for ML workflows by efficiently taking advantage of serverless infrastructures. Cirrus combines the simplicity of the serverless interface and the scalability of the serverless infrastructure (AWS Lambdas and S3) to minimize user effort. We show a design specialized for both serverless computation and iterative ML training is needed for robust and efficient ML training on serverless infrastructure. Our evaluation shows that Cirrus outperforms frameworks specialized along a single dimension: Cirrus is 100x faster than a general purpose serverless system [36] and 3.75x faster than specialized ML frameworks for traditional infrastructures [49].

Successful demonstration of the lithium-air (Li-air) battery technology, known as a potential alternative to lithium ion batteries due to its high theoretical energy density, can contribute to electrification of transportation sector as well as solar/wind powerplants to resolve their intermittency issue. The advancement of this technology requires a cathode catalyst to drive oxygen reduction and evolution reactions (ORR and OER) happening during discharge and charge processes, respectively, at high rates at low overpotentials. This can lead to low potential gap, high efficiency, and long cycle life due to reversible formation/decomposition of lithium peroxide (Li2O2) at the cathode surface. Recently developed catalysts systems such as noble metals, bimetallic catalysts, carbon-based catalysts, transition metal oxides, and transition metal dichalcogenides have been studied to achieve such performances with incremental improvements.Here, we are presenting trimolybdenum phosphide (Mo3P) nanoparticles as an earth-abundant and stable catalyst with outstanding structural and electronic properties at surface active sites studied for ORR and OER. Our electrochemical results indicate ORR and OER current densities of 7.21 mA/cm2 at 2.0 V vs Li/Li+ (ORR) and 6.85 mA/cm2 at 4.2 V vs Li/Li+ (OER) for Mo3P nanoparticles in a non-aqueous electrolyte. Tafel plot analysis for this catalyst show slopes of 35 and 38 mV/dec for ORR and OER, respectively, suggesting a faster charge transfer kinetics, as well as ORR and OER onset potentials of 4 and 5.1 mV that are the lowest values yet reported. Moreover, our turnover frequency (TOF) calculation, actual catalytic activity, indicates up to 7 times higher activity of Mo3P nanoparticles for both ORR and OER compared to state-of-the-art catalysts used for the same application. We have tested the catalytic performance of Mo3P nanoparticles in our custom designed Li-air battery cell working at the actual air environment. The results indicate that this catalyst works perfectly together with electrolyte and lithium anode to achieve an energy efficiency of 90.2% and potential gap of 350 mV at a capacity of 500 mAh/g, surpassing the performances of state-of-the-art Li-air batteries.We have also performed various characterization techniques such as scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in-situ differential electrochemical mass spectroscopy (DEMS) to elucidate the nature of the product in our battery cell. The results confirm fully reversible formation and decomposition of lithium peroxide (Li2O2) as the only discharge product. Furthermore, density functional theory (DFT) calculation suggests that the observed ORR and OER activities are due to the formation of a kinetically stable oxide overlayer on the Mo-terminated Mo3P (110) surface sites. The high performance, inexpensive catalyst found in our work can indeed contribute to development of efficient energy storage systems, specifically Li-air batteries, to speed up the global energy transition.

In recent years, the combustion of fossil fuels leads to the release of a large amount of CO2 gas, which induces the greenhouse effect and the energy crisis. To solve these problems, researchers have turned their focus to a novel Li-CO2 battery (LCB). LCB has received much attention because of its high theoretical energy density and reversible CO2 reduction/evolution process. So far, the emerging LCB still faces many challenges derived from the slow reaction kinetics of discharge products. In this review, the latest status and progress of LCB, especially the influence of the structure design of cathode catalysts on the battery performance, are systematically elaborated. This review summarizes in detail the existing issues and possible solutions of LCB, which is of high research value for further promoting the development of Li-Air battery.