Investigating the Origin of the Enhanced Sodium Storage Capacity of Transition Metal Sulfide Anodes in Ether‐Based Electrolytes

Abstract

Although ether‐based electrolytes have gradually been identified as a vital factor to achieving the excellent electrochemical performance observed in transition metal sulfide (TMS) anodes in sodium‐ion batteries (SIBs), there is still a lack of a fundamental understanding about the origin of the positive effect of ether‐based electrolytes on TMS anodes. Herein, a microspherical CoS2 anode has been taken as a representative of TMS. It has been demonstrated that the sodiation process involves not only a traditional conversion reaction taking place between solid‐state CoS2 and Na2S, but also a solid–liquid phase conversion process between active materials and soluble sodium polysulfide (Na2Sn, 2 < n < 8). More importantly, it is first revealed that the long‐term stability and the reversibility of CoS2 anode are mainly due to the solid–liquid conversion behavior, which makes bulk CoS2 gradually develop into a stable porous structure with fast Na+ transport kinetics and small stress/strain during cycling. Consequently, the CoS2 electrode delivers remarkable long‐cycle life with an ultrahigh capacity retention rate of 94.8% even after 1500 cycles at 2 A g−1 (only 2.13 mAh g−1 fading per 100 cycles) and high volumetric capacity of 949 mAh cm−3 at a high active material loading of 3.3 mg cm−2.

Modified reaction kinetics in ester-based electrolyte to boost sodium storage performance: a case study of MoS2/Ti3C2Tx hybrid

“…According to a recent study, after the initial intercalation of a conversion-type electrode, the subsequent conversion reaction between the intercalated product (solid state) and Na + will induce the generation of solid-state Na 2 S and liquid-state Na 2 S x in DEGDME. 1 To confirm the generation of liquid-state soluble Na 2 S x upon electrochemical redox, the separator obtained from the cycled cells was immersed in DEGDME or EC/DEC overnight, and ultraviolet-visible (UV-vis) spectroscopy was performed. As shown in Fig.…”

“…21 In particular, the porous structure formed upon cycling, modified ionic diffusion, and reduced charge-transfer resistance, simultaneously accelerating the reaction kinetics and enhancing the electrochemical reversibility, account for the remarkable sodium storage performance in ether-based electrolyte. 1,18…”

“…Transition-metal dichalcogenides (TMDs), which have high theoretical capacities, adjusted interlayer distances, and suitable redox potentials, have been deemed to be potential electrode materials for sodium-ion batteries (SIBs). 1–3 Among the various TMDs, molybdenum disulfide (MoS 2 ), based on its unique physical and chemical properties, possesses high electrochemical activity with a theoretical capacity of 670 mA h g −1 , and has attracted extensive attention for sodium storage. 4,5 However, the rate capability and initial coulombic efficiency (ICE) of MoS 2 -based electrodes remain challenging: (1) the volume expansion during the conversion reaction at low voltage leads to severe mechanical fracture and even pulverization, which results in instability of the solid electrolyte interface (SEI) and increased interfacial impedance; (2) the sluggish electrochemical reaction kinetics during the sodiation/desodiation of MoS 2 -based electrodes due to poor electrical conductivity, which result in degraded rate capability.…”

“…Transition-metal dichalcogenides (TMDs), which have high theoretical capacities, adjusted interlayer distances, and suitable redox potentials, have been deemed to be potential electrode materials for sodium-ion batteries (SIBs). [1][2][3] Among the various TMDs, molybdenum disulfide (MoS 2 ), based on its unique physical and chemical properties, possesses high electrochemical activity with a theoretical capacity of 670 mA h g −1 , and has attracted extensive attention for sodium storage. 4,5 However, the rate capability and initial coulombic efficiency (ICE) of MoS 2 -based electrodes remain challenging:…”

Anionic Activity in Fast-Charging Batteries: Recent Advances, Prospects, and Challenges

“…As fast-charging and large-capacity rechargeable batteries have become increasingly significant components of electric vehicles, tremendous efforts have been devoted to synergistically coupling alloying-type materials with enhanced pseudocapacitive behavior and high reaction reversibility. ,− …”