Sodium ion battery (SIBs) because of a low cost and high abundance ratios and other advantages to become the most promising of the lithium ion battery after fill object, however, due to the diffusion control dynamic hysteresis effect and larger volume expansion, the SIB in high rate and long life.

Pseudo capacitor energy storage is a kind of charge storage mode based on surface Faraday reaction mechanism, which has high energy density and high power density of double layer capacitor. Combine it into the battery system and hopefully solve the problem of high power and long life of sodium storage.

MoS2 is a kind of material which is stacked by van der Waals force and has a layered structure of graphite-like structure. The larger layer spacing is beneficial to the embedding of sodium ions. However, the large and thick plate of MoS2 formed during the charging and discharging process increases the migration distance of sodium ions, resulting in the degradation of the electrode material. In addition, the electronic conductivity of MoS2 is poor, which will further lead to polarization and reduce the utilization of electrode material.

In view of this, professor qiu js, the chang of dalian university of technology and the university of WeiShiDui Sun Xueliang professor (common) and others with carbon fiber as the basal grow high ratio and long life characteristics of nanometer ultra wide layer spacing flower MoS2 (E - MoS2 / carbon fiber). Thanks to increase the charge transfer and mass transfer, the E - MoS2 / carbon fiber electrode at up to 20 a/g under the current density of the output capacity of 104 mah/g, fully charge and discharge time is only 18.7 s, its excellent artifact capacitor charge storage capacity in the 3000 times in the process of circulation can still remained stable.

FIG. 1. (a, b) E - MoS2 / TEM images of carbon fiber, and (c) HRTEM images, (d), E - MoS2 / carbon fiber, the carbon fiber MoS2 / carbon fiber and commercial MoS2 XRD spectrum, (E) structure model of MoS2 different layer spacing, (f) of carbon fiber, E - MoS2 / carbon fiber, MoS2 / carbon fiber and commercial MoS2 Raman spectra.

Figure 2. (a) E - MoS2 / carbon fiber in the CV curves under 0.1 mV/s, (b) E - MoS2 / carbon fiber in the charge-discharge curves under 50 ma/g, (c) E - MoS2 / carbon fiber, ratio of MoS2 / carbon fiber and carbon fiber properties, (d) E - MoS2 / carbon fiber in the constant current charge and discharge curves under different current density, (E) E - MoS2 / carbon fiber, MoS2 / cycle performance of carbon fiber and carbon fiber and coulomb efficiency, (f) E - MoS2 / carbon fiber in a / 5 a/g and 10 g of cycle performance.

Electrochemical analysis showed that the capacitance contribution of 2mV/s was 89.4%. And it can provide a high energy density of up to 54.9Wh/kg when the electrode is made of commercial activated carbon (AC) as a sodium ion capacitor (SIHC). At the same time, the authors attributed their excellent electrochemical performance to the following:

The open structure of MoS2 nano-flowers can increase the contact area between electrode material and electrolyte and shorten the diffusion path of ion.

The ultra wide spacing of MoS2 can reduce ion diffusion resistance and increase the active surface area.

As a flexible substrate interwoven carbon fiber network, the electronic transmission of MoS2 nano-flowers is more smooth.

References:

Changtai Zhao, Chang Yu, Mengdi Zhang, Qian Sun, Shaofeng Li, Mohammad Norouzi Banis, Xiaotong Han, Qiang, Dong, Juan Yang, Gang Wang, Xueliang Sun, Jieshan Qiu, Enhanced sodium storage capability enabled by super wide - interlayer spacing MoS2 integrated on carbon fibers, the Nano Energy 2017, DOI: 10.1016 / org/j. anoen. 2017.08.030