Hierarchical NiCo₂S₄@NiO Core–Shell Heterostructures as Catalytic Cathode for Long‐Life Li‐O₂ Batteries

Abstract

vehicles. In a typical electrochemical reaction, the discharge product of lithium peroxide (Li 2 O 2 ) can reversibly form and decompose on cathode side during oxygen reduction reaction (ORR) and subsequent oxygen evolution reaction (OER) processes, respectively (O 2 + 2Li + + 2e − ↔ Li 2 O 2 ). [1][2][3][4] Nevertheless, several critical barriers embracing unsatisfactory charge/discharge polarization, poor rate capability, and limited cycle life make the fantastic technology far from practical application, which can be mainly attributed to the intrinsic characteristic of discharge products including insulation property and insolubilization in aprotic electrolytes. During ORR process, Li 2 O 2 precipitations clog the eversmooth passageways of reactants and passivate electrode surfaces, deteriorating electrical connection between catalysts and efficient active sites, raising charge transfer impedance. In OER process, the insulating Li 2 O 2 precipitations are knotty to be composed, delivering unsatisfactory dynamic performance and triggering higher overpotential. [5][6][7][8][9][10] It has been well established that the morphology and distribution of Li 2 O 2 determined by different growth pathway during ORR govern the battery chemistry and hence the electrochemical performance. [11][12][13] Recent works demonstrate that large-sized Li 2 O 2 aggregations (large discs, [14,15] toroids, [16][17][18][19] spheres, [20,21] etc.) contribute to large discharge capacity output during ORR but at the cost of huge charge overpotential during OER, because large sized Li 2 O 2 products do not usually well contact with active sites and are not easily decomposed, thus resulting in a larger charging voltage gap and sluggish charging kinetics. On the contrary, the formation of conformal Li 2 O 2 films or small amorphous Li 2 O 2 particles during ORR can offer much smaller charge transfer resistance and thus improve kinetics performance obviously during the following charge process. [22][23][24][25] Unfortunately, under such condition, the exposed active sites of catalyst matrix would be inactivated quickly, hence leading to a lower discharge capacity. To alleviate this contradiction between large ORR capacity and small OER voltage gap, it mainly focuses on oxygen catalytic cathode to construct elaborate hierarchical porous structures and optimize microstructure of highly efficient dual-catalystThe critical challenges of Li-O 2 batteries lie in sluggish oxygen redox kinetics and undesirable parasitic reactions during the oxygen reduction reaction and oxygen evolution reaction processes, inducing large overpotential and inferior cycle stability. Herein, an elaborately designed 3D hierarchical heterostructure comprising NiCo 2 S 4 @NiO core-shell arrays on conductive carbon paper is first reported as a freestanding cathode for Li-O 2 batteries. The unique hierarchical array structures can build up multidimensional channels for oxygen diffusion and electrolyte impregnation. A built-in interfacial potential between NiCo 2 S 4 and NiO c...

A Bifunctional Photo‐Assisted Li–O2 Battery Based on a Hierarchical Heterostructured Cathode

“…The semicircle in the high-to-medium frequency region of a Nyquist plots is assigned to the charge transfer resistance (R ct ), originating from the resistance between the electrode/electrolyte interfaces. [47] As seen in Figure 4b, the R ct for the cell under illumination was much smaller than that without illumination, giving rise to the superior interfacial charge transfer kinetics in the photo-assisted Li-O 2 cell.…”

Metal chalcogenides for potassium storage

“…Among the various categories of catalysts for Li‐O 2 batteries, metal chalcogenides have already been utilized to boost the reversible formation of Li 2 O 2 on the cathode. For example, Yin's group utilized hierarchical NiCo 2 S 4 ‐based core‐shell nanostructures as cathode catalysts for Li‐O 2 batteries . The specific capacity, discharge/charge reversibility, and cycling performance have all been improved.…”

Controlled Design of Well‐Dispersed Ultrathin MoS2 Nanosheets inside Hollow Carbon Skeleton: Toward Fast Potassium Storage by Constructing Spacious “Houses” for K Ions

“…Hollow architectures including yolk–shell, egg‐like, capsule‐like, tube‐like nanostructures have been extensively studied in the fields of drug‐controlled release, catalysis, and energy conversion . Particularly for electrode materials, loading active materials in such enclosed or half‐enclosed structures would not only avoid the exfoliation of active materials from the electrodes, but also provide enough space to alleviate the volume expansion .…”

“…Thereby, loading MoS 2 inside such hollow architectures is anticipated to construct the stable MoS 2 @C electrode materials with the weak capacity fading in the potassiation/depotassiation process. At present, several routes (mainly the selective etching template method) have been used to fabricate such hybrids . Despite proven to be effective, the multistep and complex synthetic process as well as the toxic additives for the template removal restrain their practical application.…”