Page 384 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 6 EVALUATION METHODS FOR PROPERTIES OF NANOSTRUCTURED BODY
novel technique such as Scanning Seebeck Coefficient important to analyze the electrochemical process,
Microprobe is being developed and applied to analyze including the mass transfer across the electrode sur-
the interface of semiconductor [11]. face, which must be affected by the nanoscale struc-
ture of the electrode materials. In this section, the
electrochemical method used to evaluate the proper-
References ties of the electrodes for batteries with a nanostructure
will be mentioned, with reference to literature con-
[1] Y. Suge Ed.: Thermoelectric Semiconductors (Netsuden cerning lithium ion and nickel hydrogen batteries.
Handoutai), Maki Shoten (1966).
[2] O. Yamashita: J. Appl. Phys., 89, 6241–6246 (2001). 6.5.1.1 Charge and discharge test
[3] T.C. Harman, J.H. Cahn and M.J. Logan: J. Appl. The charge/discharge test is one of the simplest meth-
Phys., 30, 1351–1359 (1959). ods used to evaluate the electrochemical properties of
the electrode for the battery. It must be noted that the
[4] J.W. Vandersande and J-P Fleurial: Proceedings of the
electrode for the battery is usually the mixture. For
11th International Conference on Thermoelectrics,
example, the cathode of a lithium ion battery consists
21–23 (1992).
of active material, like LiCoO , LiMn O and so on,
[5] K. Kishimoto, T. Koyanagi: J. Appl. Phys., 92, 2 2 4
acetylene black as an electric conductor and PVDF as
2544–2549 (2002). a binder. This mixture is pressed onto the titanium or
[6] K.F. Hsu, S. Loo, F. Guo, W. Chen, J.S. Dyck, C. Uher, SUS mesh or painted onto the Al foil as a current col-
T. Hogan, E.K. Polychroniadis, M.G. Kanatzidis: lector to prepare the practical cathode. The electro-
Science, 303, 818–821 (2004). chemical response of such an electrode must be
[7] R. Venkatasubramanian, E. Siivola, T. Colpitts, affected by many factors, each of which is difficult to
B. O’Quinn: Proceedings of the 18th International distinguish separately in terms of effect. Even the
mechanical stress in the electrode can be reflected in
Conference on Thermoelectrics, 100–103 (1999).
the electrochemical response. Therefore, the charge/
[8] R. Venkatasubramanian, E. Siivola, T. Colpitts, B.
discharge data must be discussed very carefully, even
O’Quinn: Nature, 413, 597–602 (2001).
including consideration of the cell design. Two elec-
[9] D.G. Cahill: Rev. Sci. Inst., 61, 802–808 (1990).
trode cells and three electrode cells respectively pro-
[10] T.C. Harman, P.J. Taylor, M.P. Walsh, B.E. LaForge: vide different information. The two electrode cell is
Science, 297, 2229–2232 (2002). constructed similarly to the practical cell and facili-
[11] H.K. Lyeo, A.A. Khajetoorians, L. Shi, K.P. Pipe, tates simple estimation of the total charge/discharge
R.J. Ram, A. Shakouri, C.K. Shih: Science, 303, behavior. The simplest two electrode cell construction
816–818 (2004). involves two electrodes, the anode and cathode,
immersed in an electrolyte solution in a beaker. Since
it is difficult to establish the same arrangement and
distance between the electrodes with this type of cell,
6.5 Electrochemical properties
causing low reproducibility in the data, the simple
beaker cell is infrequently used. Generally, the use of
6.5.1 Electrode reaction the coin type cell is preferred as a two electrode cell.
The electrolyte solution permeated separator is held by
There has been considerable research concerning the the electrodes in the coin cell. In this case, it must be
interface between the electrode and the electrolyte noted that the pressure applied to the electrodes must
where the electrochemical reaction takes place. For be uniform, otherwise there may be variable repro-
example, the electrochemical reaction has been basi- ducibility of the measurements or leakage of the elec-
cally studied by using gold and platinum plates as the trolyte solution. With these points in mind, a two
inert electrode. The concept of the electric double layer electrode test cell for lab use is commercially pro-
(EDL) is one of the important results from those theo- vided, with an example shown in Fig. 6.5.1. The three
retical studies. However, to date, there has been no electrode cell, meanwhile, includes a reference elec-
successfully conducted direct observation of the trode in addition to the working and counter electrodes
electrode surface on such a fine scale, because the [1, 2]. In this case, the working and counter electrodes
EDL thickness is less than several microns and the fact correspond to the cathode and anode in a two electrode
that the situation changes dynamically. Therefore, cell, while the potential of the working electrode is
attempts have been made to investigate the electro- controlled by using that of the reference electrode. The
chemical reactions by monitoring the current response electrochemical response of the working electrode can
at a certain voltage. Further, there is the case where the be measured by using the three electrode cell, the elec-
electrode itself is one of the reactants, whereby it tric circuit of which is shown in Fig. 6.5.2. The current
undergoes a redox reaction in the battery and plating which flows between the working and reference elec-
system. Because it is attractive to study these electro- trodes is so small that the reference electrode can
chemical systems from a practical perspective, it is maintain a constant potential during the measurement.

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