Preparation of Yolk‐Shell and Filled Co₉S₈ Microspheres and Comparison of their Electrochemical Properties

Abstract

In this study, we report the first preparation of phase-pure Co9S8 yolk–shell microspheres in a facile two-step process and their improved electrochemical properties. Yolk–shell Co3O4 precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co9S8 yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co9S8 microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co9S8 microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m(2) g(−1) with a mean pore size of 16 nm. The yolk–shell Co9S8 microspheres have initial discharge and charge capacities of 1008 and 767 mA h g(−1) at a current density of 1000 mA g(−1), respectively, while the filled Co9S8 microspheres have initial discharge and charge capacities of 838 and 638 mA h g(−1), respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g(−1), respectively, and the corresponding capacity retentions after the first cycle are 82% and 66%.

Hollow nanospheres of mesoporous Co 9 S 8 as a high-capacity and long-life anode for advanced lithium ion batteries

“…After 100 cycles at 200 mA g À 1 , the reversible capacity of Co 9 S 8 -650 is $ 1122 mA h g À 1 (Figure S5), much better than the previous reports (Table S1) [7,[15][16][17][18][19][20][21][22][23][24][25][26][27][28]. For example, roselike Co 9 S 8 microparticles assembled by numerous nanosheets [17], only showed a discharge capacity of 123 mA h g À 1 after 30 cycles at 50 mA g À 1 .…”

“…Electrochemical measurements show their outstanding lithiumstorage performance, $1414 mA h g À 1 after 100 cycles at a current density of 100 mA g À 1 . This result is much higher than those in literature [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Intriguingly, the cycling of these hollow nanospheres presents a typical capacity recovery, which was observed in many transitional metal oxides but less understood [11,14,29].…”

“…This capacity was promoted to $302 mA h g À 1 by flower-like CoS microparticles obtained by a solvothermal reaction [18]. Yolk-shell microspheres of Co 9 S 8 prepared by spray pyrolysis and hightemperature sulfidation, further enhanced the reversible capacity to 634 mA h g À 1 for 100 cycles at 1 A g À 1 [19]. Surface modification of sulfides by carbon is another way to improve electrochemical performances.…”

“…Cobalt sulfides as an anode have been receiving attention recently, due to their high electronic conductivity, good thermal stability and high theoretical capacity [7,[15][16][17][18][19][20][21][22][23][24][25][26][27][28]. For instance, rose-like Co 9 S 8 architectures composed of randomly dispersed nano-sheets [17], presented a reversible capacity of 123 mA h g À 1 after 30 cycles at 50 mA g À 1 .…”

Phosphorus Incorporation into Co9S8 Nanocages for Highly Efficient Oxygen Evolution Catalysis

“…Besides, the Cu 2p XPS spectrum (Figure S9, Supporting Information) shows no Cu species in P‐Co 9 S 8 , further suggesting complete removal of Cu 2 O templates, which is in consistent with the EDX result (Figure S4d, Supporting Information). N 2 adsorption–desorption measurements (Figure i) show that the P‐Co 9 S 8 nanocages possess a high specific surface area of 58 m 2 g −1 , exceeding most reported cobalt sulfides with hollow strucutre . The benefit of such high surface area can provide rich active sites for electrocatalysis.…”