On the Reliability of Sodium Co-Intercalation in Expanded Graphite Prepared by Different Methods as Anodes for Sodium-Ion Batteries

Abstract

Recent improvements of sodium ion batteries have been achieved by the use of graphitic carbon as an anode and glyme-based electrolytes. In this work, expanded graphites are prepared by thermal expansion, Broddie and Hummer's modified methods. Their structural, morphological and electrochemical properties are compared with those of the original natural graphite. XRD patterns, XPS and Raman spectra corroborate the presence of graphite oxide intermediates and reveal different reduced forms of expanded graphite which can affect the sodium insertion properties. The use of sodium triflate in diglyme enhanced the electrochemical performance in terms of delivering a flat plateau at ca. 0.65 and 0.55 V in discharge/charge cycles. The thermally expanded graphite increased the capacity and efficiency from 100 to 115 mA h g −1 and from 93 to 96% over 100 cycles when cycled at C rate as compared to natural graphite. Ex-situ XRD patterns reveal the presence of new set of reflections ascribable to sodium ordering in different stages as evidenced by the calculated Patterson diagrams. The new results described here would account for development of carbon-based material and their prospects and challenges for sodium ion battery anodes. The sodium intercalation into graphite is still one of the most interesting and unusual in the solid state chemistry of intercalation compounds. Neither ionic nor hard sphere model theory explains why the liquid phase interaction of molten sodium with graphite provides only high-stage compositions.1,2 This effect contrasts with that for other alkali metals, 3 in which first-stage graphite intercalation compounds (GICs) can be easily obtained. Udod suggested that the discrepancy between the size of sodium atoms and the distances between potential minima in the graphite sheet causes the absence of low-stage Na-GICs. 4 Graphite has a long-range-ordered layered structure where Li + ion can be easily intercalated between the graphene layers by electrochemical means. The main lithium insertion reaction occurs at a flat plateau around 0.2 V, and the capacity is 372 mA h g −1 . 5,6 Unlike, the graphite anode does not intercalate sodium to any appreciable extent. The galvanostatic curves during the full sodiation/desodiation shows a monotonic voltage curves, which capacity is lower than 35 mA h g −1 . 7,8 This normally refers to the standard electrolytes that are based on organic carbonates (EC ethylene carbonate, DMC dimethylcarbonate) and lithium salts (LiPF 6 ) or sodium salts (NaPF 6 ).In the search for alternative secondary batteries that will replace lithium ion batteries (LIBs), sodium ion batteries (SIBs) have received attention due to the following reasons: (i) abundance of sodium sources (it is the 4 th most abundant element in the earth crust), (ii) the low cost of sodium compared to lithium, especially for largescale electric storage applications, and (iii) the similar chemistry of sodium and lithium.9 So far, several issues have scoffed at the optimal performance of graphite anodes at both lithi...

Cobalt Disulfide Nanoparticles Embedded in Porous Carbonaceous Micro-Polyhedrons Interlinked by Carbon Nanotubes for Superior Lithium and Sodium Storage

“…Once more, comparing the (dis-)­charge profiles of CoS 2 -C/CNT anodes in the two different electrolytes (see Figure c,d), NaPF 6 –EC/PC shows a significantly increasing polarization when elevating the applied current, while the DME-based cell reveals a decrease of all (dis-)­charge features. According to previous literature results, the rapid capacity fading of the CoS 2 -C/CNT electrode in carbonate-based electrolyte is likely attributed to the carbon exfoliation occurring in the PC-based electrolyte. − However, the improved long-cycling life, rate capability, and reversibility of the CoS 2 -C/CNT electrode in 1 M NaPF 6 –DME electrolyte can be ascribed to (i) the formation of a more stable SEI layer and (ii) the suppressed Na-polysulfide dissolution in DME. ,− In fact, the Na-ion storage performance reported herein, especially with respect to cycling stability and rate capability, is superior compared to almost all previous studies on CoS 2 or CoS 2 -based composites, as summarized in Tables S5 and S6.…”

Graphitic Carbon Materials for Advanced Sodium‐Ion Batteries

“…Following these pioneering works, various graphitic carbon materials, including graphene foam, natural graphite, N330 carbon black, expanded graphite, carbon sheets, and graphitic mesocarbon microbead, have been cycled in ether‐based electrolytes to examine cointercalation reactions. Almost all of the materials delivered high reversible capacities, long cycle life, and remarkable high rate capabilities ( Table 1 ).…”

“…This work suggested the modification of the Na storage performance by regulating the functional groups in expanded graphite. Cabello et al studied the effect of the chemical structure and morphology of expanded graphite fabricated using different methods on the Na cointercalation properties . The expanded graphite materials were prepared by i) fast heating of graphite bisulfate or the reduction of graphite oxide using ii) Broddie's method or iii) Hummer's method, which resulted in an interlayer spacing/crystalline size of 3.388 Å/17.8 nm, 3.445 Å/6 nm, and 3.352 Å/8.46 nm, respectively.…”

The main problems and solutions in practical application of anode materials for sodium ion batteries and the latest research progress

“…Researchers have conducted many studies on how to expand the graphite layer spacing. Wen et al 8 increased the interlayer distance to 0.43 nm through oxidation and partial reduction of graphite, while retaining the long‐range ordered layered structure of graphite, which can provide a reversible capacity of 284 mAhg −1 at a current density of 20 mAg − 1 .Cabello, et al 9 prepared expanded graphite by heat treatment and compared the electrochemical properties with the original natural graphite. Compared with natural graphite, when it is cycled at a C rate, thermal expansion graphite increases capacity and efficiency by 15 mAhg −1 and 3% in 100 cycles.…”