Negative electrode materials carbon nanotubes

It was established already in the first period of works on sodium ion batteries that contrary to the lithium ion, the sodium ion is not intercalated into the interlayer space of graphite. Sodium ions penetrate nongraphitized carbon materials, but the nature of this penetration is not intercalation. In the case of oil coke, the capacity values of 90 - 95 mAh/g were obtained, which approximately corresponds to the composition of NaC24. In the case of carbon black electrodes, capacity of about 200 mAh/g was obtained. Quite suitable materials for the negative electrode could be different varieties of nanoporous hard carbon (obtained, e.g., by pyrolysis of glucose). In this case, intercalation of sodium ions is provided not only by their intercalation into the interlayer space, but also by their adsorption on the inner nanopore surface. The capacity of electrodes of nanoporous hard carbon reaches 300 mAh/g. Most recently, negative electrodes of carbon nanotubes with nearly similar sodium intercalation capacity were described. 

The characteristics of ECPs can be significantly increased by the formation of composites between ECPs and other materials, for example, carbon (including carbon nanotubes), inorganic oxides and hydroxides, and other metal compounds. Examples of some such composites and their electrochemical characteristics are given in Table 28.4. Such electrodes can be used to manufacture symmetrical devices (type I or type in) of the same positive and negative electrodes. Composite materials... 

Several types of NiO or Ni(OH)2 electrode such as flowerUke [3], mesoporous [4], nanotubes [5], and nanorod [6] were investigated as active materials for electrochemical capacitors. These Ni oxide electrodes are combined with carbon negative electrodes to construct the hybrid capacitors with high capacity and power density [2]. However, there still remaining serious problems with life cycle, reducibility, long-term stability, etc. It would need some more innovation for the practical use of these high-performance electrode materials. 

FIGURE 2.56 Typical structure of the IL inside electrified pores of the CE)C-1200 material. Blue C-C bonds, red BMI+, and green PFs. (a) Local structure near a positive surface (+0.5 V), the anionic density is enhanced, (b) A single anion in a nanotube-like pore positively polarized (+0.5 V). (c) Same as (a) but near a negative surface (-0.5 V). (Reprinted by permission from Macmillan Publishers Ltd. Nature Materials Merlet, C. et al. 2012. On the molecular origin of supercapacitance in nanoporous carbon electrodes. 11 306-310, copyright 2012.)... 

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