Engineering Hollow Porous Carbon-Sphere-Confined MoS₂ with Expanded (002) Planes for Boosting Potassium-Ion Storage

Abstract

Potassium-ion batteries (PIBs) are emerging as promising next-generation electrochemical storage systems for their abundant and low-cost potassium resource. The key point of applying PIBs is to exploit stable K-host materials to accommodate the large-sized potassium ion. In this work, a yolk−shell structured MoS 2 @hollow porous carbon-sphere composite (MoS 2 @HPCS) assembled by engineering HPCSconfined MoS 2 with expanded (002) planes is proposed for boosting potassium-ion storage. When used as a PIB anode, the as-synthesized MoS 2 @HPCS composite shows superior potassium storage performance. It delivers a reversible capacity of 254.9 mAh g −1 at 0.5 A g −1 after 100 discharge/charge cycles and maintains 126.2 mAh g −1 at 1 A g −1 over 500 cycles. The superior potassium-ion storage performance is ascribed to the elaborate yolk−shell nanoarchitecture and the expanded interlayer of the MoS 2 nanosheet, which could shorten the transport distance, enhance the electronic conductivity, relieve the volume variation, prevent the self-aggregation of MoS 2 , facilitate the electrolyte penetration, and boost the intercalation/deintercalation of K + . Moreover, the potential application of the MoS 2 @HPCS composite is also evaluated by assembled K-ion full cells with a perylenetetracarboxylic dianhydride cathode. Accordingly, the as-developed synthetic strategy can be extended to manufacture other host materials for PIBs and beyond.

Bottom‐Up Synthesis of MoS2/CNTs Hollow Polyhedron with 1T/2H Hybrid Phase for Superior Potassium‐Ion Storage

“…Obviously, there are no obvious reduction peaks appeared at ≈0.9 and ≈0.3 V in the first cycle. Generally, the peak around 0.93 V is indicating K-ions intercalation into MoS 2 layers to form KxMoS 2 , and the other reduction peak at about 0.32 V is attributed to the conversion reaction of KxMoS 2 to generate Mo and K 2 S. [26,27] According to our speculation that the disappearance of these two reduction peaks at ≈0.93 and ≈0.32 V for 1T/2H-MoS 2 /NCNHP, indicated there is no phase transformation accompanies the initial K + Figure 5. Electrochemical performance of 1T/2H-MoS 2 /NCNHP: a) initial five CV cycles at 0.1 mV s −1 and b) charge/discharge curves of 1T/2H-MoS 2 / NCNHP at 0.05 A g −1 .…”

“…The above results indicate that the 1T/2H-MoS 2 /NCNHP electrode possesses a superior K-ion storage property, which is not only better than the contrast samples but also comparable to the most recently reported MoS 2 anode materials at various current densities (Figure 5g). [1,2,[18][19][20]24,27] To explore the kinetics of the 1T/2H-MoS 2 /NCNHP electrode, CV measurement was applied at various scan rates ranging from 0.1 to 1.0 mV s −1 . All the curves show similar shapes under different scan rates (Figure 6a).…”

“…Obviously, there are no obvious reduction peaks appeared at ≈0.9 and ≈0.3 V in the first cycle. Generally, the peak around 0.93 V is indicating K‐ions intercalation into MoS 2 layers to form K x MoS 2 , and the other reduction peak at about 0.32 V is attributed to the conversion reaction of K x MoS 2 to generate Mo and K 2 S. [ 26,27 ] According to our speculation that the disappearance of these two reduction peaks at ≈0.93 and ≈0.32 V for 1T/2H‐MoS 2 /NCNHP, indicated there is no phase transformation accompanies the initial K + intercalation process because of the existence of the dominant 1T phase. And the new cathodic peak at ≈1.5 V can be ascribed to a small amount of K ions intercalation in 1T‐MoS 2 without a phase decomposition and reflects the formation of solid‐electrolyte interphase (SEI).…”

“…f) Cyclic stability of 1T/2H‐MoS 2 /NCNHP at 1.0 A g −1 (insets: the morphology of 1T/2H‐MoS 2 /NCNHP after 500 cycles). g) The potassium storage properties of the recently reported MoS 2 anode materials at various current densities (MoS 2 @rGO, [ 1 ] MoS 2 /N‐Doped‐C, [ 2 ] MoS 2 @HPCS, [ 27 ] MoS 2 /C@NDG, [ 24 ] red phosphorus/MoS 2, [ 19 ] MoS 2 @rGO‐nanoenergy, [ 18 ] and Co 9 S 8 /NSC@MoS 2 @NSC [ 20 ] ).…”

“…as spacers to prevent restacking and expand interlayer distance; [1,2,11,[16][17][18][19][20][21][22] 3) coupling with conductive materials to improve electrical conductivity; [18,23,24] 4) porous or hollow structure design to inhibit the agglomeration of MoS 2 nanosheets and buffer volume variation during the long-time charge and discharge process. [4,11,20,23,[25][26][27] For example, Lei and co-workers reported that MoS 2 nanoflowers with expanded interlayer spacing and defects show enhanced K-storage performance compared to the defect-free counterpart. [13] Wei and co-workers observed that by coupled with reduced graphene oxide sheets, the as-synthesized MoS 2 @rGO composite has an expanded interlayer distance of MoS 2 itself and delivers a high specific capacity (679 mAh g −1 at 20 mA g −1 ).…”