Resolving the Incomplete Charging Behavior of Redox-Mediated Li‑O₂ Batteries via Sustainable Protection of Li Metal Anode

Lithium–oxygen batteries (LOBs) have attracted worldwide attention due to their high specific energy. However, the poor rechargeability and cycling stability of LOBs hinders their practical use in applications. Here, we explore the incomplete charging behavior of redox-mediated LOBs operated at a feasible capacity for a practical level (3.25 mAh cm–2) and resolve it using a sustainable lithium protection strategy. The incomplete charging behavior, promoted by self-discharge of redox mediators (RMs), hampers the reversible cycling of LOBs, which was investigated through multiangle in situ and ex situ analyses. Meanwhile, the proposed lithium protection strategy, introducing an inorganic/organic hybrid artificial composite layer with a preformed stable interface between the lithium metal and the composite layer, enhances the stability of the lithium metal anode during the prolonged cycling by preventing the chemical/electrochemical interactions of RMs on the lithium metal surface, thus improving the overall rechargeability of LOBs. This work provides guidelines for the effective use of RMs with an adequate lithium protection strategy to achieve sustainable cycling of LOBs, creating a feasible approach for the practical use of LOBs with high areal capacity

Study on the Electrochemical Reaction Mechanism of NiFe₂O₄ as a High-Performance Anode for Li-Ion Batteries

Nickel ferrite (NiFe₂O₄) has been previously shown to have a promising electrochemical performance for lithium-ion batteries (LIBs) as an anode material. However, associated electrochemical processes, along with structural changes, during conversion reactions are hardly studied. Nanocrystalline NiFe₂O₄ was synthesized with the aid of a simple citric acid assisted sol–gel method and tested as a negative electrode for LIBs. After 100 cycles at a constant current density of 0.5 A g^–1 (about a 0.5 C-rate), the synthesized NiFe₂O₄ electrode provided a stable reversible capacity of 786 mAh g^–1 with a capacity retention greater than 85%. The NiFe₂O₄ electrode achieved a specific capacity of 365 mAh g^–1 when cycled at a current density of 10 A g^–1 (about a 10 C-rate). At such a high current density, this is an outstanding capacity for NiFe₂O₄ nanoparticles as an anode. Ex-situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) were employed at different potential states during the cell operation to elucidate the conversion process of a NiFe₂O₄ anode and the capacity contribution from either Ni or Fe. Investigation reveals that the lithium extraction reaction does not fully agree with the previously reported one and is found to be a hindered oxidation of metallic nickel to nickel oxide in the applied potential window. Our findings suggest that iron is participating in an electrochemical reaction with full reversibility and forms iron oxide in the fully charged state, while nickel is found to be the cause of partial irreversible capacity where it exists in both metallic nickel and nickel oxide phases

Self-Rearrangement of Silicon Nanoparticles Embedded in Micro-Carbon Sphere Framework for High-Energy and Long-Life Lithium-Ion Batteries

Despite its highest theoretical capacity, the practical applications of the silicon anode are still limited by severe capacity fading, which is due to pulverization of the Si particles through volume change during charge and discharge. In this study, silicon nanoparticles are embedded in micron-sized porous carbon spheres (Si-MCS) via a facile hydrothermal process in order to provide a stiff carbon framework that functions as a cage to hold the pulverized silicon pieces. The carbon framework subsequently allows these silicon pieces to rearrange themselves in restricted domains within the sphere. Unlike current carbon coating methods, the Si-MCS electrode is immune to delamination. Hence, it demonstrates unprecedented excellent cyclability (capacity retention: 93.5% after 500 cycles at 0.8 A g^–1), high rate capability (with a specific capacity of 880 mAh g^–1 at the high discharge current density of 40 A g^–1), and high volumetric capacity (814.8 mAh cm^–3) on account of increased tap density. The lithium-ion battery using the new Si-MCS anode and commercial LiNi_0.6Co_0.2Mn_0.2O₂ cathode shows a high specific energy density above 300 Wh kg^–1, which is considerably higher than that of commercial graphite anodes

Revealing the Reaction Mechanism of Na–O₂ Batteries using Environmental Transmission Electron Microscopy

Sodium–oxygen (Na–O₂) batteries are being extensively studied because of their higher energy efficiency compared to that of lithium oxygen (Li–O₂) batteries. The critical challenges in the development of Na–O₂ batteries include the elucidation of the reaction mechanism, reaction products, and the structural and chemical evolution of the reaction products and their correlation with battery performance. For the first time, in situ transmission electron microscopy was employed to probe the reaction mechanism and structural evolution of the discharge products in Na–O₂ batteries. The discharge product was featured by the formation of both cubic and conformal NaO₂. It was noticed that the impingement of the reaction product (NaO₂) led to particle coarsening through coalescence. We investigated the stability of the discharge product and observed that the reaction product NaO₂ was stable in the case of the solid electrolyte. The present work provides unprecedented insight into the development of Na–O₂ batteries

Revealing the Reaction Mechanism of Na–O₂ Batteries using Environmental Transmission Electron Microscopy

Sodium–oxygen (Na–O₂) batteries are being extensively studied because of their higher energy efficiency compared to that of lithium oxygen (Li–O₂) batteries. The critical challenges in the development of Na–O₂ batteries include the elucidation of the reaction mechanism, reaction products, and the structural and chemical evolution of the reaction products and their correlation with battery performance. For the first time, in situ transmission electron microscopy was employed to probe the reaction mechanism and structural evolution of the discharge products in Na–O₂ batteries. The discharge product was featured by the formation of both cubic and conformal NaO₂. It was noticed that the impingement of the reaction product (NaO₂) led to particle coarsening through coalescence. We investigated the stability of the discharge product and observed that the reaction product NaO₂ was stable in the case of the solid electrolyte. The present work provides unprecedented insight into the development of Na–O₂ batteries

Revealing the Reaction Mechanism of Na–O₂ Batteries using Environmental Transmission Electron Microscopy

Sodium–oxygen (Na–O₂) batteries are being extensively studied because of their higher energy efficiency compared to that of lithium oxygen (Li–O₂) batteries. The critical challenges in the development of Na–O₂ batteries include the elucidation of the reaction mechanism, reaction products, and the structural and chemical evolution of the reaction products and their correlation with battery performance. For the first time, in situ transmission electron microscopy was employed to probe the reaction mechanism and structural evolution of the discharge products in Na–O₂ batteries. The discharge product was featured by the formation of both cubic and conformal NaO₂. It was noticed that the impingement of the reaction product (NaO₂) led to particle coarsening through coalescence. We investigated the stability of the discharge product and observed that the reaction product NaO₂ was stable in the case of the solid electrolyte. The present work provides unprecedented insight into the development of Na–O₂ batteries

Ruthenium-Based Electrocatalysts Supported on Reduced Graphene Oxide for Lithium-Air Batteries

Ruthenium-based nanomaterials supported on reduced graphene oxide (rGO) have been investigated as air cathodes in non-aqueous electrolyte Li-air cells using a TEGDME-LiCF₃SO₃ electrolyte. Homogeneously distributed metallic ruthenium and hydrated ruthenium oxide (RuO₂·0.64H₂O), deposited exclusively on rGO, have been synthesized with average size below 2.5 nm. The synthesized hybrid materials of Ru-based nanoparticles supported on rGO efficiently functioned as electrocatalysts for Li₂O₂ oxidation reactions, maintaining cycling stability for 30 cycles without sign of TEGDME-LiCF₃SO₃ electrolyte decomposition. Specifically, RuO₂·0.64H₂O-rGO hybrids were superior to Ru-rGO hybrids in catalyzing the OER reaction, significantly reducing the average charge potential to ∼3.7 V at the high current density of 500 mA g^–1 and high specific capacity of 5000 mAh g^–1

Stabilization of Lithium-Metal Batteries Based on the in Situ Formation of a Stable Solid Electrolyte Interphase Layer

Lithium (Li) metals have been considered most promising candidates as an anode to increase the energy density of Li-ion batteries because of their ultrahigh specific capacity (3860 mA h g^–1) and lowest redox potential (−3.040 V vs standard hydrogen electrode). However, unstable dendritic electrodeposition, low Coulombic efficiency, and infinite volume changes severely hinder their practical uses. Herein, we report that ethyl methyl carbonate (EMC)- and fluoroethylene carbonate (FEC)-based electrolytes significantly enhance the energy density and cycling stability of Li-metal batteries (LMBs). In LMBs, using commercialized Ni-rich Li­[Ni_0.6Co_0.2Mn_0.2]­O₂ (NCM622) and 1 M LiPF₆ in EMC/FEC = 3:1 electrolyte exhibits a high initial capacity of 1.8 mA h cm^–2 with superior cycling stability and high Coulombic efficiency above 99.8% for 500 cycles while delivering a unprecedented energy density. The present work also highlights a significant improvement in scaled-up pouch-type Li/NCM622 cells. Moreover, the postmortem characterization of the cycled cathodes, separators, and Li-metal anodes collected from the pouch-type Li/NCM622 cells helped identifying the improvement or degradation mechanisms behind the observed electrochemical cycling

A Metal-Free, Lithium-Ion Oxygen Battery: A Step Forward to Safety in Lithium-Air Batteries

A preliminary study of the behavior of lithium-ion-air battery where the common, unsafe lithium metal anode is replaced by a lithiated silicon–carbon composite, is reported. The results, based on X-ray diffraction and galvanostatic charge–discharge analyses, demonstrate the basic reversibility of the electrochemical process of the battery that can be promisingly cycled with a rather high specific capacity

Influence of Temperature on Lithium–Oxygen Battery Behavior

In this Letter we report an electrochemical and morphological study of the response of lithium–oxygen cells cycled at various temperatures, that is, ranging from −10 to 70 °C. The results show that the electrochemical process of the cells is thermally influenced in an opposite way, that is, by a rate decrease, due to a reduced diffusion of the lithium ions from the electrolyte to the electrode interface, at low temperature and a rate enhancement, due to the decreased electrolyte viscosity and consequent increased oxygen mobility, at high temperature. In addition, we show that the temperature also influences the crystallinity of lithium peroxide, namely of the product formed during cell discharge