A Highly Reversible Long‐Life Li–CO2 Battery with a RuP2‐Based Catalytic Cathode

Rechargeable Li–CO₂ batteries have attracted worldwide attention due to the capability of CO₂ capture and superhigh energy density. However, they still suffer from poor cycling performance and huge overpotential. Thus, it is essential to explore highly efficient catalysts to improve the electrochemical performance of Li–CO₂ batteries. Here, phytic acid (PA)‐cross‐linked ruthenium complexes and melamine are used as precursors to design and synthesize RuP₂ nanoparticles highly dispersed on N, P dual‐doped carbon films (RuP₂‐NPCFs), and the obtained RuP₂‐NPCF is further applied as the catalytic cathode for Li–CO₂ batteries. RuP₂ nanoparticles that are uniformly deposited on the surface of NPCF show enhanced catalytic activity to decompose Li₂CO₃ at low charge overpotential. In addition, the NPCF its with porous structure in RuP₂‐NPCF provides superior electrical conductivity, high electrochemical stability, and enough ion/electron and space for the reversible reaction in Li–CO₂ batteries. Hence, the RuP₂‐NPCF cathode delivers a superior reversible discharge capacity of 11951 mAh g^?1, and achieves excellent cyclability for more than 200 cycles with low overpotentials (<1.3 V) at the fixed capacity of 1000 mAh g^?1. This work paves a new way to design more effective catalysts for Li–CO₂ batteries.     

A Co‐Doped MnO2 Catalyst for Li‐CO2 Batteries with Low Overpotential and Ultrahigh Cyclability

Li‐CO₂ batteries can not only capture CO₂ to solve the greenhouse effect but also serve as next‐generation energy storage devices on the merits of economical, environmentally‐friendly, and sustainable aspects. However, these batteries are suffering from two main drawbacks: high overpotential and poor cyclability, severely postponing the acceleration of their applications. Herein, a new Co‐doped alpha‐MnO₂ nanowire catalyst is prepared for rechargeable Li‐CO₂ batteries, which exhibits a high capacity (8160 mA h g^?1 at a current density of 100 mA g^?1), a low overpotential (≈0.73 V), and an ultrahigh cyclability (over 500 cycles at a current density of 100 mA g^?1), exceeding those of Li‐CO₂ batteries reported so far. The reaction mechanisms are interpreted depending on in situ experimental observations in combination with density functional theory calculations. The outstanding electrochemical properties are mostly associated with a high conductivity, a large fraction of hierarchical channels, and a unique Co interstitial doping, which might be of benefit for the diffusion of CO₂, the reversibility of Li₂CO₃ products, and the prohibition of side reactions between electrolyte and electrode. These results shed light on both CO₂ fixation and new Li‐CO₂ batteries for energy storage.     

A High‐Capacity O2‐Type Li‐Rich Cathode Material with a Single‐Layer Li2MnO3 Superstructure

A high capacity cathode is the key to the realization of high‐energy‐density lithium‐ion batteries. The anionic oxygen redox induced by activation of the Li₂MnO₃ domain has previously afforded an O3‐type layered Li‐rich material used as the cathode for lithium‐ion batteries with a notably high capacity of 250–300 mAh g^?1. However, its practical application in lithium‐ion batteries has been limited due to electrodes made from this material suffering severe voltage fading and capacity decay during cycling. Here, it is shown that an O2‐type Li‐rich material with a single‐layer Li₂MnO₃ superstructure can deliver an extraordinary reversible capacity of 400 mAh g^?1 (energy density: ≈1360 Wh kg^?1). The activation of a single‐layer Li₂MnO₃ enables stable anionic oxygen redox reactions and leads to a highly reversible charge–discharge cycle. Understanding the high performance will further the development of high‐capacity cathode materials that utilize anionic oxygen redox processes.     

Controlling the Placement of Spherical Nanoparticles in Electrically Driven Polymer Jets and its Application to Li‐Ion Battery Anodes

Employing circumferentially uniform air flow through the sheath layer of the concentric coaxial nozzle, the gas‐assisted electrospinning (GAES) utilizes both high electric field and controlled air flow to produce nanofibers. The ability to tailor the distribution of various nanofillers (1.85–12.92 vol% of spherical SiO₂ and Si nanoparticles) in a polyvinyl alcohol jet is demonstrated by varying airflow rates in GAES. The distribution of nanofillers is measured from transmission electron microscopy and is analyzed using an image processing technique to perform the dispersion area analysis and obtain the most probable separation between nanoparticles using fast Fourier transform (FFT). The analysis in this study indicates an additional 350% improvement in dispersion area with the application of high but controlled airflow, and a 75 percent decrease in separation between nanoparticles from the FFT. The experiments in this study are in good agreement with a coarse‐grained MD simulation prediction for a polymer nanocomposite system subjected to extensional deformation. Lastly, utilizing the sheath layer air flow in production of Li‐battery anode material, a 680 mAh g^?1 improvement is observed in capacity for nanofibers spun via GAES compared to ES at the same Si NP loading, which is associated with better dispersion of the electrochemically active nanoparticles.     

Protecting the Li‐Metal Anode in a Li–O2 Battery by using Boric Acid as an SEI‐Forming Additive

The Li–O₂ battery (LOB) is considered as a promising next‐generation energy storage device because of its high theoretic specific energy. To make a practical rechargeable LOB, it is necessary to ensure the stability of the Li anode in an oxygen atmosphere, which is extremely challenging. In this work, an effective Li‐anode protection strategy is reported by using boric acid (BA) as a solid electrolyte interface (SEI) forming additive. With the assistance of BA, a continuous and compact SEI film is formed on the Li‐metal surface in an oxygen atmosphere, which can significantly reduce unwanted side reactions and suppress the growth of Li dendrites. Such an SEI film mainly consists of nanocrystalline lithium borates connected with amorphous borates, carbonates, fluorides, and some organic compounds. It is ionically conductive and mechanically stronger than conventional SEI layer in common Li‐metal‐based batteries. With these benefits, the cycle life of LOB is elongated more than sixfold.     

One‐Step Route Synthesized Co2P/Ru/N‐Doped Carbon Nanotube Hybrids as Bifunctional Electrocatalysts for High‐Performance Li–O2 Batteries

The large‐scale commercial application of lithium–oxygen batteries (LOBs) is overwhelmed by the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) associated with insoluble and insulated Li₂O₂. Herein, an elaborate design on a highly catalytic LOBs cathode constructed by N‐doped carbon nanotubes (CNT) with in situ encapsulated Co₂P and Ru nanoparticles is reported. The homogeneously dispersed Co₂P and Ru catalysts can effectively modulate the formation and decomposition behavior of Li₂O₂ during discharge/charge processes, ameliorating the electronically insulating property of Li₂O₂ and constructing a homogenous low‐impedance Li₂O₂/catalyst interface. Compared with Co/CNT and Ru/CNT electrodes, the Co₂P/Ru/CNT electrode delivers much higher oxygen reduction triggering onset potential and higher ORR and OER peak current and integral areas, showing greatly improved ORR/OER kinetics due to the synergistic effects of Co₂P and Ru. Li–O₂ cells based on the Ru/Co₂P/CNT electrode demonstrate improved ORR/OER overpotential of 0.75 V, excellent rate capability of 12 800 mAh g^?1 at 1 A g^?1, and superior cycle stability for more than 185 cycles under a restricted capacity of 1000 mAh g^?1 at 100 mA g^?1. This work paves an exciting avenue for the design and construction of bifunctional catalytic cathodes by coupling metal phosphides with other active components in LOBs.     

Ruthenium Nanoparticles on Cobalt‐Doped 1T′ Phase MoS2 Nanosheets for Overall Water Splitting

2D MoS₂ nanostructures have recently attracted considerable attention because of their outstanding electrocatalytic properties. The synthesis of unique Co–Ru–MoS₂ hybrid nanosheets with excellent catalytic activity toward overall water splitting in alkaline solution is reported. 1T′ phase MoS₂ nanosheets are doped homogeneously with Co atoms and decorated with Ru nanoparticles. The catalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is characterized by low overpotentials of 52 and 308 mV at 10 mA cm^?2 and Tafel slopes of 55 and 50 mV decade^?1 in 1.0 m KOH, respectively. Analysis of X‐ray photoelectron and absorption spectra of the catalysts show that the MoS₂ well retained its metallic 1T′ phase, which guarantees good electrical conductivity during the reaction. The Gibbs free energy calculation for the reaction pathway in alkaline electrolyte confirms that the Ru nanoparticles on the Co‐doped MoS₂ greatly enhance the HER activity. Water adsorption and dissociation take place favorably on the Ru, and the doped Co further catalyzes HER by making the reaction intermediates more favorable. The high OER performance is attributed to the catalytically active RuO₂ nanoparticles that are produced via oxidation of Ru nanoparticles.     

Self‐Assembled 3D Foam‐Like NiCo2O4 as Efficient Catalyst for Lithium Oxygen Batteries

A self‐assembled 3D foam‐like NiCo₂O₄ catalyst has been synthesized via a simple and environmental friendly approach, wherein starch acts as the template to form the unique 3D architecture. Interestingly, when employed as a cathode for lithium oxygen batteries, it demonstrates superior bifunctional electrocatalytic activities toward both the oxygen reduction reaction and the oxygen evolution reaction, with a relatively high round‐trip efficiency of 70% and high discharge capacity of 10 137 mAh g^?1 at a current density of 200 mA g^?1, which is much higher than those in previously reported results. Meanwhile, rotating disk electrode measurements in both aqueous and nonaqueous electrolyte are also employed to confirm the electrocatalytic activity for the first time. This excellent performance is attributed to the synergistic benefits of the unique 3D foam‐like structure and the intrinsically high catalytic activity of NiCo₂O₄.     

Strongly Coupled Carbon Nanosheets/Molybdenum Carbide Nanocluster Hollow Nanospheres for High‐Performance Aprotic Li–O2 Battery

A highly efficient oxygen electrode is indispensable for achieving high‐performance aprotic lithium–O₂ batteries. Herein, it is demonstrated that strongly coupled carbon nanosheets/molybdenum carbide (α‐MoC_1?x) nanocluster hierarchical hybrid hollow spheres (denoted as MoC_1?x/HSC) can work well as cathode for boosting the performance of lithium–O₂ batteries. The important feature of MoC_1?x/HSC is that the α‐MoC_1?x nanoclusters, uniformly incorporated into carbon nanosheets, can not only effectively prevent the nanoclusters from agglomeration, but also help enhance the interaction between the nanoclusters and the conductive substrate during the charge and discharge process. As a consequence, the MoC_1?x/HSC shows significantly improved electrocatalytic performance in an aprotic Li–O₂ battery with greatly reduced charge and discharge overpotentials and long cycle stability. The ex situ scanning electron microscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy studies reveal that the mechanism for the high‐performance Li–O₂ battery using MoC_1?x/HSC as cathode is that the incorporated molybdenum carbide nanoclusters can make oxygen reduction on their surfaces easy, and finally form amorphous film‐like Li‐deficient Li₂O₂ with the ability to decompose at a low potential. To the best of knowledge, the MoC_1?x/HSC of this paper is among the best cathode materials for lithium–O₂ batteries reported to date.