Carbon-Free Cathodes: A Step Forward in the Development of Stable Lithium-Oxygen Batteries

Electrodeposition Technologies for Li-Based Batteries: New Frontiers of Energy Storage

Electrodeposition induces material syntheses on conductive surfaces, distinguishing it from the widely used solid-state technologies in Li-based batteries. Electrodeposition drives uphill reactions by applying electric energy instead of heating. These features may enable electrodeposition to meet some needs for battery fabrication that conventional technologies can rarely achieve. The latest progress of electrodeposition technologies in Li-based batteries is summarized. Each component of Li-based batteries can be electrodeposited or synthesized with multiple methods. The advantages of electrodeposition are the main focus, and they are discussed in comparison with traditional technologies with the expectation to inspire innovations to build better Li-based batteries. Electrodeposition coats conformal films on surfaces and can control the film thickness, providing an effective approach to enhancing battery performance. Engineering interfaces by electrodeposition can stabilize the solid electrolyte interphase (SEI) and strengthen the adhesion of active materials to substrates, thereby prolonging the battery longevity. Lastly, a perspective of future studies on electrodepositing batteries is provided. The significant merits of electrodeposition should greatly advance the development of Li-based batteries.

Stable Voltage Cutoff Cycle Cathode with Tunable and Ordered Porous Structure for Li-O2 Batteries

Ordered porous RuO₂ materials with various pore structure parameters are prepared via a hard-template method and are used as the carbon-free cathodes for Li-O₂ batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO₂ on electrochemical performance are systematically studied. Results indicate that specific surface area and pore size determine the specific capacity and round-trip efficiency of Li-O₂ batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li⁺ and O₂ , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO₂ , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li-O₂ battery based on the RuO₂ cathode with an average pore size of 16 nm (RuO₂ -16) exhibits a high round-trip efficiency of ≈75.6% and an excellent cycling stability of up to 70 cycles at 100 mA g^-1 with a voltage window of 2.5-4.0 V. The superior performance of RuO₂ -16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO₂ can effectively reduce parasitic reactions compared with carbon materials.

Strategies toward High-Performance Cathode Materials for Lithium-Oxygen Batteries

Rechargeable aprotic lithium (Li)-O₂ batteries with high theoretical energy densities are regarded as promising next-generation energy storage devices and have attracted considerable interest recently. However, these batteries still suffer from many critical issues, such as low capacity, poor cycle life, and low round-trip efficiency, rendering the practical application of these batteries rather sluggish. Cathode catalysts with high oxygen reduction reaction (ORR) and evolution reaction activities are of particular importance for addressing these issues and consequently promoting the application of Li-O₂ batteries. Thus, the rational design and preparation of the catalysts with high ORR activity, good electronic conductivity, and decent chemical/electrochemical stability are still challenging. In this Review, the strategies are outlined including the rational selection of catalytic species, the introduction of a 3D porous structure, the formation of functional composites, and the heteroatom doping which succeeded in the design of high-performance cathode catalysts for stable Li-O₂ batteries. Perspectives on enhancing the overall electrochemical performance of Li-O₂ batteries based on the optimization of the properties and reliability of each part of the battery are also made. This Review sheds some new light on the design of highly active cathode catalysts and the development of high-performance lithium-O₂ batteries.

MnCo2 O4 /MoO2 Nanosheets Grown on Ni foam as Carbon- and Binder-Free Cathode for Lithium-Oxygen Batteries

Carbon is usually used as cathode material for Li-O₂ batteries. However, the discharge product, such as Li₂ O₂ and LiO₂ , could react with carbon to form an insulating lithium carbonate layer, resulting in cathode passivation and capacity fading. To solve this problem, the development of non-carbon cathodes is highly desirable. Herein, we successfully synthesized MnCo₂ O₄ (MCO) nanoparticles anchored on porous MoO₂ nanosheets that are grown on Ni foam (current collector) (MCO/MoO₂ @Ni), acting as a carbon- and binder-free cathode for Li-O₂ batteries, in an attempt to improve the electrical conductivity, electrocatalytic activity, and durability. This MCO/MoO₂ @Ni electrode delivers excellent cyclability (more than 400 cycles) and rate performance (voltage gap of 0.75 V at 5000 mA g^-1 ). Notably, the battery with this electrode exhibits a high energy efficiency (higher than 85 %). The advanced electrochemical performance of MCO/MoO₂ @Ni can be attributed to its high electrical conductivity, excellent stability, and outstanding electrocatalytic activity. This work offers a new strategy to fabricate high-performance Li-O₂ batteries with non-carbon cathode materials.

Reduced Co3O4 nanowires with abundant oxygen vacancies as an efficient free-standing cathode for Li–O2 batteries

The reduced Co₃O₄ cathode with abundant oxygen vacancies significantly improves the battery's cycling stability.

Complete Decomposition of Li2CO3 in Li-O2 Batteries Using Ir/B4C as Noncarbon-Based Oxygen Electrode

Instability of carbon-based oxygen electrodes and incomplete decomposition of Li₂CO₃ during charge process are critical barriers for rechargeable Li-O₂ batteries. Here we report the complete decomposition of Li₂CO₃ in Li-O₂ batteries using the ultrafine iridium-decorated boron carbide (Ir/B₄C) nanocomposite as a noncarbon based oxygen electrode. The systematic investigation on charging the Li₂CO₃ preloaded Ir/B₄C electrode in an ether-based electrolyte demonstrates that the Ir/B₄C electrode can decompose Li₂CO₃ with an efficiency close to 100% at a voltage below 4.37 V. In contrast, the bare B₄C without Ir electrocatalyst can only decompose 4.7% of the preloaded Li₂CO₃. Theoretical analysis indicates that the high efficiency decomposition of Li₂CO₃ can be attributed to the synergistic effects of Ir and B₄C. Ir has a high affinity for oxygen species, which could lower the energy barrier for electrochemical oxidation of Li₂CO₃. B₄C exhibits much higher chemical and electrochemical stability than carbon-based electrodes and high catalytic activity for Li-O₂ reactions. A Li-O₂ battery using Ir/B₄C as the oxygen electrode material shows highly enhanced cycling stability than those using the bare B₄C oxygen electrode. Further development of these stable oxygen-electrodes could accelerate practical applications of Li-O₂ batteries.

New Insights into the Instability of Discharge Products in Na-O2 Batteries

Sodium-oxygen batteries currently stimulate extensive research due to their high theoretical energy density and improved operational stability when compared to lithium-oxygen batteries. Cell stability, however, needs to be demonstrated also under resting conditions before future implementation of these batteries. In this work we analyze the effect of resting periods on the stability of the sodium superoxide (NaO2) discharge product. The instability of NaO2 in the cell environment is demonstrated leading to the evolution of oxygen during the resting period and the decrease of the cell efficiency. In addition, migration of the superoxide anion (O2(-)) in the electrolyte is observed and demonstrated to be an important factor affecting Coulombic efficiency.