Discharge manganese dioxide

The cathode reaction involves reduction of silver oxide to metallic silver [7440-22-4J. The reaction is a two-phase, heterogeneous reaction producing a substantially constant voltage during discharge. Some manganese dioxide may be added to the cathode, as in the case of mercury oxide cells. 

Fig. 18. Discharge curves for miniature 2inc—silver oxide batteries (-), and 2inc—manganese dioxide batteries (—) (21).

Figure 35. Self-discharge characteristics of the CR17335SE lithium-manganese dioxide battery.

The design of a AA-size alkaline manganese dioxide cell is shown in Fig. 1 (Sec. 3.1). Primary and secondary alkaline batteries are constructed in the same way and can be manufactured on essentially the same machinery. The separator material, electrode formulation, and the Mn02 Zn balance are different. Rechargeable cells are zinc-limited to prevent a discharge beyond the first electron-equivalent of the MnOz reduction. The electrolyte is 7-9 mol L KOH. The electrode reactions are ... 

As shown in Fig. 8, three types of polarization exist during the discharge of porous MnOa. The battery active EMD or CMD (chemical manganese dioxide) is highly porous and the concentration polarization due to the pH change, r (ApH), is very important. Kozawa studied the three types of... 

Soon it became evident that the zinc anode, working in both cases under capacity-limiting conditions, causes severe troubles too. Whereas in the zinc/air system the anode automatically limits the discharge (because access to oxygen from the air is practically unlimited), the anode limitation in zinc/manganese dioxide cells has another reason Kordesch and co-workers... 

Depending on the composition of the active materials and on the manganese dioxide type employed, the OCV of freshly manufactured zinc-carbon cells with salt electrolyte varies between 1.55 and 1.85 V. It decreases during discharge and formation of the variable-composition mass. Upon prolonged storage of undischarged batteries, their OCV also decreases. 

Compared with the Leclanche batteries, alkaline manganese dioxide batteries offer better performance at high discharge currents and lower temperatures and a better shelf life. They are more expensive than Leclanche batteries, but their cost per unit of energy is competitive and resources of raw materials are sufficient for mass production of these batteries. 

Another example for reactions with the insertion of protons is the cathodic reduction of manganese dioxide, which occnrs dnring discharge of the positive electrodes in zinc-manganese dioxide batteries. This reaction can be formulated as... 

A lead-acid storage battery is only one type of battery, however. Different batteries use different metals and electrolytes to make them work. For example, alkaline batteries (the ones found in flashlights, toys, and portable electronic devices) contain powdered zinc and manganese dioxide as their electrodes. They use an electrolyte made of an alkaline solution of potassium hydroxide. Most alkaline batteries have a finite amount of chemicals in them. Once the chemicals react with one another, they are used up, and the battery goes dead (is discharged) and cannot be recharged. 

Shao-Hom Y., Hackney S. A., Comilsen B. C., Structural characterization of heat-treated electrolytic manganese dioxide and topotactic transformation of discharge products in the Li-Mn02 cells, J. Electrochem. Society, (1997) 144, 3147-3153. 

The observed higher rate of mass transfer in nonstoichiometric oxides makes it possible to operate at discharge current densities on the order of 2 - 5 mA/cm2, which is several times greater than that used with the conventional manganese dioxide. Thus, the purposeful disordering of structure of a cathode material of manganese dioxide allows to utilize such power sources in extreme conditions - for element discharge at a low... 

The name Leclanche cell is given to the familiar primary system consisting of a zinc anode, manganese dioxide cathode and an electrolyte of ammonium chloride and zinc chloride dissolved in water. The alternative designation zinc-carbon ceir is broader and includes the so-called zinc chloride system which, due to a different electrolyte composition, is characterized by a different discharge mechanism. The Leclanche cell may be written as... 

Calculations of the emf of cells based on these reactions provide values within the wide range of 1.5-1.7 V, characteristic of undischarged cells formed with different samples of manganese dioxide and electrolyte pH. However, during the discharge of practical cells, inhomogeneities in the solution and cathode phases may produce a much more complicated reaction sequence, as will be discussed below. 

---