Warum Lithium-Sauerstoff-Batterien versagen: Parasitäre chemische Reaktionen und ihr synergistischer Effekt

Boosting Cycling Stability and Rate Capability of Li-CO2 Batteries via Synergistic Photoelectric Effect and Plasmonic Interaction

Sluggish CO₂ reduction/evolution kinetics at cathodes seriously impede the realistic applications of Li-CO₂ batteries. Herein, synergistic photoelectric effect and plasmonic interaction are introduced to accelerate CO₂ reduction/evolution reactions by designing a silver nanoparticle-decorated titanium dioxide nanotube array cathode. The incident light excites energetic photoelectrons/holes in titanium dioxide to overcome reaction barriers, and induces the intensified electric field around silver nanoparticles to enable effective separation/transfer of photogenerated carriers and a thermodynamically favorable reaction pathway. The resulting Li-CO₂ battery demonstrates ultra-low charge voltage of 2.86 V at 0.10 mA cm^-2 , good cycling stability with 86.9 % round-trip efficiency after 100 cycles, and high rate capability at 2.0 mA cm^-2 . This work offers guidance on rational cathode design for advanced Li-CO₂ batteries and beyond.

High-Efficiency and Stable Li-CO2 Battery Enabled by Carbon Nanotube/Carbon Nitride Heterostructured Photocathode

Li-CO₂ batteries are explored as promising power systems to alleviate environmental issues and to implement space applications. However, sluggish cathode kinetics of CO₂ reduction/evolution result in low round-trip efficiency and poor cycling stability of the fabricated energy-storage devices. Herein, we design a heterostructued photocathode comprising carbon nanotube and carbon nitride to accelerate cathode reactions of a Li-CO₂ battery under illumination. Benefiting from the unique defective structure of carbon nitride and favorable interfacial charge transfer, the photocathode effectively harvests ultraviolet-visible light to generate abundant photoexcited carriers and coordinates energetic photoelectrons/holes to participate in the discharge/charge reactions, leading to efficient photo-energy utilization in decreasing reaction barriers and enhancing thermodynamic reversibility of Li-CO₂ battery. The resulting battery delivers a high round-trip efficiency of 98.8 % (ultralow voltage hysteresis of 0.04 V) and superior cycling stability (86.1 % efficiency retention after 100 cycles).

Enabling Lithium Metal Anode in Nonflammable Phosphate Electrolyte with Electrochemically Induced Chemical Reactions

Lithium metal anode holds great promises for next-generation battery technologies but is notoriously difficult to work with. The key to solving this challenge is believed to lie in the ability of forming stable solid-electrolyte interphase (SEI) layers. To further address potential safety issues, it is critical to achieve this goal in nonflammable electrolytes. Building upon previous successes in forming stable SEI in conventional carbonate-based electrolytes, here we report that reversible Li stripping/plating could be realized in triethyl phosphate (TEP), a known flame retardant. The critical enabling factor of our approach was the introduction of oxygen, which upon electrochemical reduction induces the initial decomposition of TEP and produces Li₃ PO₄ and poly-phosphates. Importantly, the reaction was self-limiting, and the resulting material regulated Li plating by limiting dendrite formation. In effect, we obtained a functional SEI on Li metal in a nonflammable electrolyte. When tested in a symmetric Li∥Li cell, more than 300 cycles of stripping/plating were measured at a current density of 0.5 mA cm^-2 . Prototypical Li-O₂ and Li-ion batteries were also fabricated and tested to further support the effectiveness of this strategy. The mechanism by which the SEI forms was studied by density functional theory (DFT), and the predictions were corroborated by the successful detection of the intermediates and products.

Electrolytes for Rechargeable Lithium-Air Batteries

Lithium-air batteries are promising devices for electrochemical energy storage because of their ultrahigh energy density. However, it is still challenging to achieve practical Li-air batteries because of their severe capacity fading and poor rate capability. Electrolytes are the prime suspects for cell failure. In this Review, we focus on the opportunities and challenges of electrolytes for rechargeable Li-air batteries. A detailed summary of the reaction mechanisms, internal compositions, instability factors, selection criteria, and design ideas of the considered electrolytes is provided to obtain appropriate strategies to meet the battery requirements. In particular, ionic liquid (IL) electrolytes and solid-state electrolytes show exciting opportunities to control both the high energy density and safety.

Towards an Understanding of Li2 O2 Evolution in Li-O2 Batteries: An In Operando Synchrotron X-ray Diffraction Study

One of the major challenges in developing high-performance Li-O₂ batteries is to understand the Li₂ O₂ formation and decomposition during battery cycling. In this study, this issue was investigated by synchrotron radiation powder X-ray diffraction. The evolution of Li₂ O₂ morphology and structure was observed under actual electrochemical conditions of battery operation. By quantitatively tracking Li₂ O₂ during discharge and charge, a two-step process was suggested for both growth and oxidation of Li₂ O₂ owing to different mechanisms during two stages of both oxygen reduction reaction and oxygen evolution reaction. From an observation of the anisotropic broadening of Li₂ O₂ in XRD patterns, it was inferred that disc-like Li₂ O₂ grains are formed rapidly in the first step of discharge. These grains can stack together so that they facilitate the nucleation and growth of toroidal Li₂ O₂ particles with a LiO₂ -like surface, which could cause parasitic reactions and hinder the formation of Li₂ O₂ . During the charge process, Li₂ O₂ is firstly oxidized from the surface, followed by a delithiation process with a faster oxidation of the bulk by stripping the interlayer Li atoms to form an off-stoichiometric intermediate. This fundamental insight brings new information on the working mechanism of Li-O₂ batteries.