2D SnSe Cathode Catalyst Featuring an Efficient Facet‐Dependent Selective Li₂O₂ Growth/Decomposition for Li–Oxygen Batteries

Abstract

during charge. [5][6][7] Unfortunately, some technological hurdles limit the practical utilization of LOBs, including high overpotentials, poor cycling performance, low capacity much below the theoretical value, and low round-trip efficiency. [1] These critical issues are closely connected to the inferior electronic/ionic conductivity of the inactive discharge product Li 2 O 2 , which results in sluggish reaction kinetics, strong redox reaction intermediates, and side reactions between carbon and electrolyte/solid products. [4,[8][9][10][11] Highly efficient cathode materials for reversible formation/ decomposition (ORR/OER) of discharge products determine the electrochemical performance of LOBs to a great extent. [8,12] On the other hand, the reaction kinetics on the cathode catalyst are not only dominated by the Li 2 O 2 formation/decomposition process, but also the adsorption/ desorption of absorbates such as O 2 , Li + , and LiO 2 . [2,[13][14][15][16][17][18] A highly efficient cathode catalyst should possess both high active catalytic capability for the ORR/OER process and appropriate adsorption ability to ensure smooth reaction kinetics. [19,20] Materials with a 2D layered structure have received considerable attention for use in catalytic, electronic and optoelectronic devices [21][22][23][24] due to their unique properties including a large surface area, [25] flexible stack layers, [26] electron confinement effect, [27] high carrier mobility, and thickness-tunable bandgap modulation. [28] Recently, 2D materials were theoretically and 2D materials are attracting much attention in the field of cathode catalysts for lithium-oxygen batteries (LOBs) due to their layered structure, unique electronic properties, and high stability. However, different stacking layer structures trigger different catalytic capabilities in LOBs. In this work, tin selenide nanosheets with a black phosphorus-like 2D structure are synthesized and used as the cathode catalyst for LOBs. SnSe nanosheets with exposed stack (200) facets and stack edge facets exhibit superior specific capacity over 20 783 mAh g −1 and ultralong cycle stability over 380 cycles at 500 mA g −1 in LOBs. This demonstrates that the growth of discharge products is mainly concentrated on the 2D surface (200) facets, rather than the stack edge facets. Experimental and theoretical studies reveal that the confined adsorption of Li 2 O 2 on the stack edge facets of SnSe, due to the 2D layer structure and the unique electron distribution, restricts the growth of discharge products. The 2D surface facets of SnSe benefit for the formation and stabilization of LiO 2 intermediates, leading to the efficient formation/ decomposition of discharge products. The findings provide in-depth insight into the elusive electrocatalytic mechanism for 2D layer-structures materials in LOBs.

A self-assembled nanoflower-like Ni5P4@NiSe2 heterostructure with hierarchical pores triggering high-efficiency electrocatalysis for Li–O2 batteries

“…The high-resolution XPS spectrum of Se 3d (figure 2(e)) splits into two-component peaks at about 54.5 and 53.5 eV, related to Se 3d 3/2 and Se 3d 1/2 of Se 2− . The Se 3d peak of Ni 5 P 4 @NiSe 2 is normally accompanied by a 58.5 eV characteristic peak assigned to the Se-O bond, confirming that the surfaces of some Se species were oxidized to SeO x during the synthesis route [44,66]. As can be seen in the high-resolution XPS spectrum of P 2p in figure 2(f), the peak of Ni 5 P 4 @NiSe 2 heterostructure at 129.35 eV is ascribed to the Ni-P bond, and the peak at 133.7 eV demonstrates the presence of oxidation on the material surfaces [55,71].…”

“…Besides, the excellent electrical conductivity of the heterostructure can accelerate the charge transfer during the charge/discharge processes and enhance the electrochemical reaction kinetics [78,79]. More importantly, the unique heterostructure shows a significant effect on the electron redistribution and disordered atomic arrangement, which can provide additional active sites to improve the ORR/OER bifunctional catalytic activity [66]. Additionally, the Ni (3)…”

Bucket effect on high-performance Li–O2 batteries based on P-doped 3D NiO microspheres with conformal growth of discharge products

“…The cathode reaction phase diagrams of LiO 2 and Li 2 O 2 were developed to further investigate their stability during the reaction processes and the related effect on the cathode potentials. 75,76 As shown in Fig. 7a, LiO 2 is unstable up to 2.87 V on the NiO (100) plane.…”

Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

“…Rechargeable Li-air or Na-air batteries are considered as promising electrochemical energy storage devices due to the high theoretical energy density, but a key major challenge for practical applications is the requirement of high voltage, especially for the charging process. [276][277][278] Catalysts play an important role in reducing the overpotentials in the 2e processes for both ORR and OER. The lack of a breakthrough in practical applications is perhaps the poor understanding of how a catalyst works under the discharge (ORR) and charge (OER) conditions, especially how the catalyst's surface chemistry correlates with the surface species at the nanoscale and atomic scale.…”