PDF Publication Title:
Text from PDF Page: 037
Review Article Chem Soc Rev 3.1.1.3. Non graphitic carbon (graphene). Graphene, unique two-dimensional carbon materials, has great physical and chemical advantages such as a large surface area, superior electronic con- ductivity, and chemical stability.267 Such advantages of graphene can bring shorter paths for fast ion diffusion and produce a large exposed surface offering more ion insertion channels.268 Therefore, for LIBs and SIBs, graphene can be considered as an anode material for energy-storage systems255,269–274 (Fig. 21b). Moreover, graphene or reduced graphene oxide (RGO) help to improving the Li and Na storage capability in its composite anodes. Recently, Wang et al. demonstrated the reversible sodium ion storage performances in reduced graphene oxide (RGO).274 RGO possesses higher electrical conductivity and active sites with large interlayer distances and provides a disordered struc- ture enabling it to store a larger amount of Na+ ions. In their study, RGO anodes exhibited a moderate specific capacity of 141 mA h g1 at 40 mA g1 with stable cycle retentions for over 1000 cycles. Ding et al. synthesised different kinds of few-layer graphene at different carbonization temperatures (600–1400 1C) and investigated the Na+ ion storage mechanism in their graphene structure.275 At a higher carbonization temperature of 1100 1C, they obtained an optimized highly ordered pseudo- graphic structure having a large interlayer spacing of 0.388 nm, which exhibited promising Na+ insertion performances. On the other hand, Datta et al. reported that the presence of defects enhances the adsorption of Na atoms in graphene sheets.276 However, such defects of graphene represent a serious draw- back such as low Coulombic efficiency that may cause Na metal plating on the rGO surfaces.255 3.1.1.4. Heteroatom doping. As an effective strategy to enhance the electrochemical properties of carbonaceous materials as anodes, heteroatom (such as N, B, S and P) doped hard carbon and graphene (or graphene liked materials) are introduced.277–291 Hetero atom doping into a carbon structure tends to create a defect site to absorb Na+ ions and improves the electrode– electrolyte interaction by functionalizing the carbon surface. Commonly, nitrogen doping into a carbon structure significantly improves ion transport and charge-transfer processes.279,280 Wang et al. proposed a 3D interconnected structure of free- standing flexible films composed of nitrogen-doped porous nanofibers that exhibited 212 mA h g1 at 5 A g1 with stable capacity retentions of 99% after 7000 cycles282 (Fig. 23a). In a recent work, sulfur-doped disordered carbon was proposed as an anode material for SIBs. Sulfur doping into the carbon structure provided additional reaction sites for accommodation of Na+ and/or contributing to facile ion diffusion by enlarging the interlayer distance. Li et al. synthesized a sulfur-doped disordered carbon that has a high sulfur doping level (B26.9%) and a unique 3D coral-like structure. The as-prepared sulfur-doped carbon exhibited a high reversible capacity of 516 mA h g1 with excellent rate capability as well as superior cyclability for 1000 cycles288 (Fig. 23b). 3.1.1.5. Biomass derivatives. As mentioned above, disordered carbon appears to be the most suitable anode material for SIBs. co-relationships between the physico-chemical properties and the electrochemical properties with commercially available porous and non-porous carbon materials (porous carbon: Timrex 100, 300, 500 and activated carbon, non-porous carbon: graphite). The highest surface area (1041 m2 g1) of activated carbon and the highest pore volume (1.008 cm3 g1) of Timrex 500 show the low reversibility with Na+ ions. Meanwhile, their templated carbon controlled by microstructural approaches minimized the diffusion lengths within the electrode (surface area: 346 m2 g1, pore volume: 0.798 cm3 g1). As a result, the carbon matrix showed excellent electrochemical activity for Na+ ions. Their results imply that high capacity and rate capabilities cannot be simply achieved by enlarging the surface area or by increasing the porosity. On the other hand, Tsai et al. further confirmed the reaction process through an ab initio study showing that a larger interlayer distance is not the only factor that helps Na intercalation. Additionally, the vacancy defects (MV: mono-vacancy and DV: di-vacancy) in hard carbon can greatly enhance the Na+ ion intercalation because of the strong ionic binding energy between the Na+ ions and the defects, which effectively overcomes the van der Waals interaction.248 Further, Bommier et al. discussed the new storage mechanism in the sloping region (as a function of the charge–discharge curve), which can be explained through Na+ ion storage at defect sites.250 They also confirmed that Na+ ions can be intercalated into the hard carbon lattice particularly in the low voltage plateau region. These findings suggest that the Na+ storage is related to a three-step process (Fig. 22d) rather than the two-step storage mechanism proposed in the card-house model (Fig. 22e); (i) Na+ ions are adsorbed at defective sites in the slope-voltage region, (ii) Na+ ions are intercalated in the hard carbon lattice, and (iii) Na+ ions are adsorbed at the pore surface in the plateau region. Such research results show that the Na+ insertion mecha- nism into a disordered structure is still controversial. Therefore, further theoretical and experimental investigation should be conducted to clarify the related reaction mechanism for devel- opment of hard carbon materials. To date, hard carbons have been the most widely used carbon source of SIB anodes and have been proved to significantly improve the electrochemical performance of SIBs. However, there are a lot of challenges facing the development of hard carbon anodes for practical applications. The reversibility of the hard carbon was found to depend on the carbon precursor, particle sizes and manufacturing processes. And, the appropriate low pore volumes and surface areas can achieve the higher reversible capacities. The suitable additives and electrolytes are highly desir- able for reversibility of Na+ storage. Therefore, based on a number of previous studies, we should consider some factors, including particle sizes, additives, electrolytes, vacancy defects and porosity measurements, to develop the high irreversible capacity and high rate capability in hard carbons. Furthermore, we should investi- gate the relationship between the electrochemical characteristics of hard carbon and solid electrolyte interphase (SEI) layer formation. At the same time, the computational works such as DFT calculation and ab initio calculation should be conducted to predict and support the experimental results. View Article Online 3564 | Chem. Soc. Rev., 2017, 46, 3529--3614 This journal is © The Royal Society of Chemistry 2017 Open Access Article. Published on 28 March 2017. Downloaded on 7/1/2019 3:41:21 AM. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.PDF Image | Sodium-ion batteries present and future
PDF Search Title:
Sodium-ion batteries present and futureOriginal File Name Searched:
Sodium-ion batteries present and future.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Salt water flow battery technology with low cost and great energy density that can be used for power storage and thermal storage. Let us de-risk your production using our license. Our aqueous flow battery is less cost than Tesla Megapack and available faster. Redox flow battery. No membrane needed like with Vanadium, or Bromine. Salgenx flow battery
| CONTACT TEL: 608-238-6001 Email: greg@salgenx.com | RSS | AMP |