Discharge Curves and Electrochemical Reactions

Ri and R2 indicate the actual discharge ranges in practical cells. 

Both Swinkels et al. [7] and Chabre and Pannetier [8] described the process of EMD reduction as three overlapping processes. Recently Donne etal. reported [9] that the presence of Bi(OH)3 on the EMD surface modified the discharge curve considerably and the rechargeability was increased. Formation of the birnessite 

Structure from EMD and Bi(OH)3 or Bi203 (mechanically mixed with EMD) [10] is the cause of the increase in rechargeability. 

These results indicate that the potential of Mn02 can change, depending on the surface condition, by as much as 18 mV. This is important for obtaining the AF value. 

Since the pH change 7 (ApH) is practically zero for the discharge in 9 mol KOH solution, we can assume that t] + tjc (solid) is the same for the two solutions (9molL KOH and 25% ZnCh). Therefore, the difference in the polarization values (in Tables 4.1 and 4.2) is Tj(ApH), where 

The basic electrochemical properties of EMD are summarized schematically in Fig. 2 fl] based on the original work by Kozawa et al. [2-5]. The electrolytic Mn02 discharges in two steps in 9 mol L KOH. The reaction during each step is shown below. 

In ZnClj solutions (with or without NH4CI), Mn02 discharges as shown in Fig. 2(B). The first 25% (from a to b ) is essentially the same Eq. (1) and the essential part of curve b c is Eq. (3)  

The electrode potential should be a reflection of the AF value of the oxide, representing its total energy. However, Kozawa and Sasaki reported [12] that surface con- 

---

Murphy et al. made an extensive study of a number of vanadium oxides and discovered the excellent electrochemical behavior of the partially reduced vanadium oxide, VeOis, which reacts with up to 1 LiA/. They also recognized that the method of preparation, which determines the V 0 ratio, critically controls the capacity for reaction with lithium. The structure consists of alternating double and single sheets of vanadium oxide sheets made up of distorted VOe octahedra. A variety of sites are available for lithium intercalation, which if filled sequentially would lead to the various steps seen in the discharge curve. The lattice first expands along the c-axis and then along the b-axis. Thomas et ai 87 91 an in-depth study of the complex... 

A variety of experimental techniques are used to study electrochemical and battery reactions (34,42—44). The most common are the direct measurement of the instantaneous current-voltage characteristics or power curve and the discharge curve at various dischaige rates. Indeed, the dischaige performance of a typical battery is characterized by these curves as depicted in Figure 6. The characteristics of the power curve varies depending on the state of charge of the battery. 

On the first cycle, passivation layers are formed on the surface of the electrodes. These layers have been shown to result from the reaction of the electrolyte with the electrode surface. The passivation layers contain lithium that is no longer electrochemically active, thus their formation results in irreversible capacity, an undesirable property of all current materials that occurs largely on the first cycle. The capacity difference between the charge and discharge curves in Fig. 35.20 results from irreversible capacity. 

---