MOF-Derived CoSe2@N-Doped Carbon Matrix Confined in Hollow Mesoporous Carbon Nanospheres as High-Performance Anodes for Potassium-Ion Batteries

Abstract

In this work, a novel vacuum-assisted strategy is proposed to homogenously form Metal–organic frameworks within hollow mesoporous carbon nanospheres (HMCSs) via a solid-state reaction. The method is applied to synthesize an ultrafine CoSe2 nanocrystal@N-doped carbon matrix confined within HMCSs (denoted as CoSe2@NC/HMCS) for use as advanced anodes in high-performance potassium-ion batteries (KIBs). The approach involves a solvent-free thermal treatment to form a Co-based zeolitic imidazolate framework (ZIF-67) within the HMCS templates under vacuum conditions and the subsequent selenization. Thermal treatment under vacuum facilitates the infiltration of the cobalt precursor and organic linker into the HMCS and simultaneously transforms them into stable ZIF-67 particles without any solvents. During the subsequent selenization process, the “dual confinement system”, composed of both the N-doped carbon matrix derived from the organic linker and the small-sized pores of HMCS, can effectively suppress the overgrowth of CoSe2 nanocrystals. Thus, the resulting uniquely structured composite exhibits a stable cycling performance (442 mAh g−1 at 0.1 A g−1 after 120 cycles) and excellent rate capability (263 mAh g−1 at 2.0 A g−1) as the anode material for KIBs.

Investigation of the potassium‐ion storage mechanism of nickel selenide materials and rational design of nickel selenide‐C yolk‐shell structure for enhancing electrochemical properties

“…40 The C 1s spectrum could be fitted to several peaks at 284.0, 284.6, 285.6, and 288.5 eV, which were assigned to C═C, C C,C O, and O C═O bonds, respectively, as displayed in Figure 6C. 41,42 Furthermore, in the Raman spectrum of NiSe x @C, the two peaks located at 1354 and 1602 cm À1 corresponded to the D band (related to disordered characteristics) and G band (related to graphitic characteristics), respectively, as shown in Figure 6D. [43][44][45][46] The I D /I G ratio (0.99) suggested that the carbon in the carbon nanospheres was partially graphitized by post-treatment at 700 C. 47,48 The thermogravimetric (TG) curves of NiSe x @C and bare NiSe x are represented in Figure S7.…”

Metal–organic framework-derived nitrogen-doped carbon-confined CoSe2 anchored on multiwalled carbon nanotube networks as an anode for high-rate sodium-ion batteries

“…5k shows the electrochemical impedance spectrum (EIS) of the CoSe 2 @NC/MWCNTs electrode at different electrochemical states during the first discharge/charge cycle. Based on the fitting results of ex situ EIS (Table S4†), the values of R ct gradually decreased during the sodiation, which might be due to the formation of ultrafine Co. 64 When charging, the impedance undergoes a negligible change, implying that the CoSe 2 @NC/MWCNTs electrode is quite stable in the (de)sodiation process.…”

Double‐shell and yolk‐shell structured ZnSe ‐carbon nanospheres as anode materials for high‐performance potassium‐ion batteries

“…During the initial discharging, R tot exhibited a continuous decrease, which could be a reflection of the transition between large crystals and ultrafine nanocrystals, as verified by the HR-TEM image (Figure 5B). 47 In the subsequent charging, R tot increased as the depotassiation proceeded. This resistance increase was due to the structural strain caused by the phase transformation to ZnSe nanocrystals.…”

“…The decreasing tendency continued to 1.0 V owing to the SEI nucleation as a stable surface deposit. 47 After 1.0 V, D K+ exhibited an increasing trend, because of the generation of ultrafine KZn 13 and K 2 Se nanocrystals. 47 The diffusion coefficient decreased as the depotassiation proceeded, which was related to the increase in R tot corresponding to the structural strain during the phase transformation.…”

“…47 After 1.0 V, D K+ exhibited an increasing trend, because of the generation of ultrafine KZn 13 and K 2 Se nanocrystals. 47 The diffusion coefficient decreased as the depotassiation proceeded, which was related to the increase in R tot corresponding to the structural strain during the phase transformation. 33 The galvanostatic intermittent titration technique (GITT) was employed to better understand the potassiumion storage mechanism of ZnSe by evaluating the K + diffusion coefficient (D K + ).…”