Nanostructured Conductive Metal Organic Frameworks for Sustainable Low Charge Overpotentials in Li–Air Batteries

Abstract

promising solution since it offers the highest theoretical energy density, that can substantially outperform Li-ion batteries. [1][2][3][4][5][6] Recently, Li-O 2 batteries have attracted a significant attention in various applications such as electrified transportation and smart grid systems; however, on the path of their practical use, there still remain many obstacles. The sluggish kinetics of the governing reactions during discharge and charge impose high overpotentials that result in low round trip efficiency. [7,8] Moreover, an inefficient decomposition of solid discharge products (Li 2 O 2 ) and its accumulation on the surface of the cathode lead to poor cycling (early failure) in these systems. [9,10] To address these issues, discovery of new cathode materials with outstanding functionalities is essential. In this context, metal organic frameworks (MOFs) are promising platforms owing to their high porosity, large surface area, highly ordered structure, and tunable chemical composition. These characteristics make MOFs an ideal candidate to be investigated as electrode materials in electrochemical energy applications [11][12][13] and especially rechargeable batteries. [14][15][16] However, traditional MOFs are still far from practical cathode materials due to their insulating nature stemming from the redox-inactive organic ligands and low-energy electron transfer pathways. [15,[17][18][19] Lithium-oxygen batteries are among the most attractive alternatives for future electrified transportation. However, their practical application is hindered by many obstacles. Due to the insulating nature of Li 2 O 2 product and the slow kinetics of reactions, attaining sustainable low charge overpotentials at high rates becomes a challenge resulting in the battery's early failure and low round trip efficiency. Herein, outstanding characteristics are discovered of a conductive metal organic framework (c-MOF) that promotes the growth of nanocrystalline Li 2 O 2 with amorphous regions. This provides a platform for the continuous growth of Li 2 O 2 units away from framework, enabling a fast discharge at high current rates. Moreover, the Li 2 O 2 structure works in synergy with the redox mediator (RM). The conductivity of the amorphous regions of the Li 2 O 2 allows the RM to act directly on the Li 2 O 2 surface instead of catalyst edges and then transport through the electrolyte to the Li 2 O 2 surface. This direct charge transfer enables a small charge potential of <3.7 V under high current densities (1-2 A g −1 ) sustained for a long cycle life (100-300 cycles) for large capacities (1000-2000 mAh g −1 ). These results open a new direction for utilizing c-MOFs towards advanced energy storage systems.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202102902.

Size-Dependent Effects in Fullerene-Based Catalysts for Nonaqueous Li–Air Battery Applications

“…Similarly, consecutive addition of Li to Li 2 O 2 can also result in the formation of Li 3 O 2 followed by Li 4 O 2 as well. We have considered different intermediates such as Li 3 O 2 , Li 3 O 4 , Li 4 O 2 , and Li 4 O 4 owing to the fact that the major ORR product Li 2 O 2 can undergo multiple nucleation reactions, leading to the formation of these intermediates, which is supported by previously reported studies. , …”

Advances of Electroactive Metal–Organic Frameworks

“…Cathode materials based on MOFs in Li-O 2 batteries are attractive. Monometallic MOFs [445][446][447][448][449][450][451] and bimetallic MOFs [452][453][454] have been reported to be promising. For instance, a 2D Mn MOF constructed by H 2 BDC, L1, and MnCl 2 •4H 2 O as cathodes exhibited a discharge-specific capacity of 9464 mAh g −1 and 1000 mAh g −1 with a life span of 200 cycles (Figure 18a-c).…”

Metal‐Organic Framework‐Based Lithium‐Oxygen Batteries

“…Majidi et al. synthesized a conductive MOF of copper tetrahydroxyquinone (Cu‐THQ), and it was exfoliated into 2D nanoflakes (NFs) and work as the cathode catalyst for LOBs [8b] . The TEM images of Cu‐THQ clearly show the open pores in Figure 5f.…”