High-Energy Density Li-O2 Battery with a Polymer Electrolyte-Coated CNT Electrode via the Layer-by-Layer Method

Low-Impedance Hybrid Carbon Structures on SiOX: A Sequential Gas-Phase Coating Approach

Carbon coating on SiOX surface is crucial for enhancing initial Coulombic efficiency (ICE) and cycling performance in batteries, while also buffering volume expansion. Despite its market prevalence, the effects of the carbon layer's quality and structure on the electrochemical properties of SiOX remain underexplored. This study compares carbon layers produced via gas-phase and solid-phase coating methods, introducing an innovative technique that sequentially uses two gases to develop a low-impedance hybrid carbon structure. In this approach, C3H8 is first deposited to create a short-range, vertically ordered carbon architecture, followed by C2H2 to establish a long-range, layered structure, effectively filling the gaps. This results in a dense hybrid carbon layer characterized by minimal defects, high crystallinity, and excellent electronic conductivity. The dominant vertical configuration enhances Li-ion migration. The SiO@C3H8@C2H2 prepared through this method yields a specific surface area of 1.14 m2 g⁻¹ and a high reversible capacity of 1574.9 mAh g⁻¹, alongside an ICE of 83.7%. It showcases remarkable cycling stability, retaining 86.6% capacity after 1000 cycles at room temperature, and performs effectively under varied temperatures and discharging conditions. This low-impedance carbon structure provides a significant reference for other anodes that also require a carbon layer.

Influence of Electrolyte Saturation on the Performance of Li-O2 Batteries

Electrolyte saturation can strongly affect the Li-O2 battery performance. However, it is unclear to what extent saturation reduction will impact the battery capacity. In this study, we investigated the influence of electrolyte saturation and distribution within a porous positive electrode on the deep discharge-charge capacities and cycling stability. The study used both models and experiments to investigate the change of electrolyte distribution, double-layer capacitance, ohmic resistance, and O2 concentration in the positive electrode at different electrolyte saturations. Results revealed that electrodes with 60% electrolyte saturation achieved almost the same maximum discharge (6.38 vs 6.76 mAh/cm2) and charge (5.52 vs 5.65 mAh/cm2) capacities with fully saturated electrodes. The partially wet positive electrode (40% saturation) obtained more cycles than the electrode with 100% saturation before the discharge capacity dropped below the cutoff point. However, the electrode with 40% saturation had a low average charging efficiency of 88.76%, whereas the fully saturated electrode obtained 98.96% charging efficiency. Moreover, the fully wet positive electrode had the lowest overpotential during cycling (1.26-1.39 V). The measured electrochemically active surface areas showed that even 40% saturation could sufficiently wet the positive electrode surface and obtain a double-layer capacitance (18.12 mF) similar to that with 100% saturation (20.4 mF). Furthermore, a considerable increase in O2 concentration at wetted surface areas was observed for the electrolyte saturation of less than 60% due to the significantly higher O2 diffusivity in the gas phase.

Recent advances and interfacial challenges in solid-state electrolytes for rechargeable Li-air batteries

Among the promising batteries for electric vehicles, rechargeable Li-air (O2) batteries (LABs) have risen keen interest due to their high energy density. However, safety issues of conventional nonaqueous electrolytes remain the bottleneck of practical implementation of LABs. Solid-state electrolytes (SSEs) with non-flammable and eco-friendly properties are expected to alleviate their safety concerns, which have become a research focus in the research field of LABs. Herein, we present a systematic review on the progress of SSEs for rechargeable LABs, mainly focusing on the interfacial issues existing between the SSEs and electrodes. The discussion highlights the challenges and feasible strategies for designing suitable SSEs for LABs.

RuO2-Incorporated Co3O4 Nanoneedles Grown on Carbon Cloth as Binder-Free Integrated Cathodes for Tuning Favorable Li2O2 Formation

Developing ideal Li-O₂ batteries (LOBs) requires the discharge product to have a large quantity, have large contact area with the cathode, and not passivate the porous surface after discharge, which put forward high requirement for the design of cathodes. Herein, combining the rational structural design and high activity catalyst selection, minor amounts of RuO₂-incorporated Co₃O₄ nanoneedles grown on carbon cloth are successfully synthesized as binder-free integrated cathodes for LOBs. With this unique design, plenty of electron-ion-oxygen tri-phase reaction interface is created, the side reaction from carbon is isolated, and oxygen reduction reaction/oxygen evolution reaction (OER) kinetics are significantly facilitated. Upon discharge, film-like Li₂O₂ is observed growing on the needle surface first and eventually ball-like Li₂O₂ particles form at each tip of the needle. The cathode surface remains porous after discharge, which is beneficial to the OER and is rare in the previous reports. The battery exhibits a high specific discharge capacity (7.64 mAh cm^-2) and a long lifespan (500 h at 0.1 mA cm^-2). Even with a high current of 0.3 mA cm^-2, the battery achieves a cycling life of 200 h. In addition, punch-type LOBs are fabricated and successfully operated, suggesting that the cathode material can be utilized in ultralight, flexible electronic devices.

Platinum Nanocrystals Embedded in Three-Dimensional Graphene for High-Performance Li-O2 Batteries

Graphene is considered as a promising cathode candidate for Li-O₂ batteries because of its excellent electronic conductivity and oxygen adsorption capacity. However, for Li-O₂ batteries, the self-stacking effect caused by two-dimensional (2D) structural properties of graphene is not conducive to the rapid oxygen transport and mass transfer process, thereby affecting the electrode kinetics. Here, we successfully prepared three-dimensional (3D) graphene with different scales by plasma-enhanced chemical vapor deposition and physical pulverization strategies, in which CH₄ is the carbon source and H₂/Ar mixed gas is the etching gas. Meanwhile, we fabricated 3D graphene-based Pt nanocatalysts by an ultraviolet-assisted construction strategy and then applied them in Li-O₂ batteries. Systematic studies reveal a special relevance between electrochemical performance and graphene particle size, and the smaller-sized 3D graphene can better maintain the microstructure distribution in both the Pt embedding process and electrochemical applications, which is beneficial to the transport of oxygen and Li ions, lowering the decomposition energy barrier of Li₂O₂, and further obtaining reduced charge overpotential (0.22 V) and prolonged cycle life for Li-O₂ batteries. Finally, we anticipate that this work could promote the practical application of 2D materials and larger-sized 3D materials in Li-O₂ batteries.

Material balance in the O2 electrode of Li-O2 cells with a porous carbon electrode and TEGDME-based electrolytes

This work figures out the material balance of the reactions occurring in the O₂ electrode of a Li–O₂ cell, where a Ketjenblack-based porous carbon electrode comes into contact with a tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte under more practical conditions of less electrolyte amount and high areal capacity. The ratio of electrolyte weight to cell capacity (E/C, g A h⁻¹) is a good parameter to correlate with cycle life. Only 5 cycles were obtained at an areal capacity of 4 mA h cm⁻² (E/C = 10) and a discharge/charge current density of 0.4 mA cm⁻², which corresponds to the energy density of 170 W h kg⁻¹ at a complete cell level. When the areal capacity was decreased to half (E/C = 20) by setting a current density at 0.2 mA cm⁻², the cycle life was extended to 18 cycles. However, the total electric charge consumed for parasitic reactions was 35 and 59% at the first and the third cycle, respectively. This surprisingly large amount of parasitic reactions was suppressed by half using redox mediators at 0.4 mA cm⁻² while keeping a similar cycle life. Based on by-product distribution, we will propose possible mechanisms of TEGDME decomposition and report a water breathing behavior, where H₂O is produced during charge and consumed during discharge.

The material balance in the O₂ electrode of a Li–O₂ cell with a Ketjenblack-based porous carbon electrode and a tetraethylene glycol dimethyl ether-based electrolyte under more practical conditions of less electrolyte amount and high areal capacity.