A Battery Deconstruction Study

Neena Ravindran, Mariam Hoseini,
Arun Shankaran, Syed Sajid Ahmad and Aaron Reinholz
Center for Nanoscale Science and Engineering (CNSE)
North Dakota State University (NDSU), Fargo ND

In many applications, power is a controlling factor for size and cost. With increased demand for portable electronics like laptops, cell phones, and MP3 players that are smaller and flatter, the demand for thin and small form factor power sources has also risen. CNSE, therefore, explored commercially-available batteries with focus on thin-film batteries and small form-factor batteries. In order to gain understanding of the design, layout and the materials considerations, a battery deconstruction study was carried out. The main interest in looking at the construction of these batteries was to understand how the different layers had been deposited on the flexible substrate. Another objective was to attempt to identify the different components of the battery. There was interest in obtaining information about the specific components that are used to prepare the electrode materials.

The work focuses on the construction of an off-the-shelf thin battery. Several instrumental techniques were employed including image analysis, X-ray diffraction (XRD), and Energy dispersive spectroscopy (EDS). Image analysis was conducted to obtain an idea of the layout to prevent any safety-related incidents while disassembling the battery. It also provided a rough estimate of the battery layout. XRD and EDS were used to obtain compositional information about the electrode materials.

Chemistry
Analyses of the battery components showed that the battery comprised zinc as anode and manganese dioxide as cathode. Each cell in general, produces a voltage of 1.5 V.  A conventional cylindrical alkaline-manganese cell differs from the zinc-carbon cell in the use of concentrated potassium hydroxide as the electrolyte which is selected due to its high electrical conductance. Another difference is that the negative zinc electrode consists of finely-divided zinc powder packed around a current collector positioned at the center of the cell. The third difference in the cell configuration wherein electrolytic MnO2 and the fine graphite powder are packed outside the zinc negative and separator, and are in contact with nickel-plated steel can. The overall chemical reaction that operates in this system is:

Zn + 2MnO2 + 2H2Oà Zn (OH)2 + 2MnO.OH. [1]

Image Analysis
Optical and x-ray images were obtained before sectioning the battery, shown in Figures 1 and 2 respectively. From the images, it was clear that there were at least three distinct layers. The dimensions of different layers were determined and are listed in Table 1. Although the information was obtained on the dimensions of different layers, it was not possible to obtain definitive information about the thickness of different battery components/layers from the optical/x-ray imaging technique.

Table 1. Dimensions of different layers

Figure 1. (a) Front and (b) side view of battery.

Figure 2. Results from the image analysis of the battery.

Battery Deconstruction Methodology
The battery was sectioned and the different layers/components were separated and placed in separate sample bags and labeled. The battery construction was found to be bipolar wherein the anode and cathode components are laid one on top of the other. There were at least three distinct layers within the battery: the anode, the cathode and the separating filter paper interspersed between the two electrode layers. The separating filter paper layer was impregnated with what appeared to be the electrolyte that was in a gel form.

X-Ray Diffraction
Samples were studied using XRD in an attempt to characterize the composition of different layers. Samples from what were considered to be different components of the cell were used for analysis. Perhaps due to the amorphous nature of the materials used, hardly any useful information could be obtained. However, from the results, the following components were identified: Graphitic Carbon, Mn and MnxOx.
Very limited information could be obtained from XRD, but perhaps a modified sampling technique could help in obtaining useful information. Better characterization may be possible if a cleaner separation of layers can be achieved. Another factor could be that since this technique is meant for crystallographic analysis, the amorphous nature of the components could be interfering with the characterization.

Energy Dispersive Spectroscopy (EDS)
EDS is used to identify and quantify elemental composition of small areas. When a material is bombarded with an electron beam such as in a scanning electron microscope, characteristic X-rays are produced. These X-rays are detected by an energy dispersive spectrometer, which is a solid state device that discriminates among X-ray energies. This was the second tool that was used to analyze the composition.
Information obtained from EDS for samples are compiled in table 2 (rows 1 to 7). The components that were analyzed were the positive and negative tabs, two different sides which were assumed to be the anode and cathode.

Table 2. Results from EDS analysis

It was seen that the tabs mainly showed the presence of elemental C (Table 2,  rows 1 to 2). It would be useful to get further information of the exact nature of the carbon used and it is expected to be a very highly conductive carbon. The next major element found was Cl and it could be the deliquescent material and the electro-active soluble material as described in example 1 of US Patent 5,652,043 [3]. A deliquescent material is a hygroscopic material and its role is to keep the cell moisturized at all times. An electro-active material provides the required ionic conductivity.

Analysis of the sides of the battery indicated only trace amounts of Mn and absence of Zn as seen in Table 2 (rows 3 to 4). There must be anode and cathode materials present for the battery to function. From the elements obtained from different parts, none qualified as the cathode or anode material. We decided to look at the material on the filter paper to evaluate if the electrode materials were actually deposited on the filter paper. Analysis of the composition of the material on the filter paper revealed the first traces of Zn and Mn and this can be seen in Table 2 (rows 3 to 4).

However, these elements were still present in trace quantities and so we decided to delve deeper into the layers of the filter paper since this technique is highly dependant on the area being sampled. For further investigations, we cut deeper into the material deposited on the filter paper on both sides and used these samples for EDS. The results are compiled in Table 2 (rows 6 to 7). As can be seen in this table, the presence of Zn and Mn was confirmed. On taking a closer look at what was concluded to be the anode layer, it appeared that it was actually two layers and their compositions were found be as outlined in Table 2 (rows 8 to 9). The results show that the first layer contains zinc whereas the bottom layer is predominantly carbon.

These studies additionally indicated the presence of trace quantities of other elements such as S, Si, Ca, Na and Ba.  These elements are typically added to improve battery performance to deal with factors such as concentration polarization, gassing and so on.

Conclusion
Based on the experimental results, the following conclusions are made:

• The coated tabs on the battery contain carbon.
• The different layers of the battery are co-facially placed, i.e., they are overlaid.
• The anode and cathode layers have a carbon layer on them.
• The anode and the cathode are deposited on different sides of a filter paper or such material.
• The electrolytes are in the form of a deliquescent material and possibly zinc chloride in this battery.

Acknowledgments
We would like to acknowledge Eric Jarabek of CMRL at North Dakota State University for help with the XRD and X-ray imaging studies and Scott Payne of Electron Microscopy Center at North Dakota State University for the EDX data.

DMEA Acknowledgement
This material is based on research sponsored by the Defense Microelectronics Activity under agreement numbers H94003-07-0701. The United States Government is authorized to reproduce and distribute reprints for government purpose, notwithstanding any copyright notation thereon.

References
[1] Handbook of Batteries, III Edition, Editors: Linden D., Reddy, T.B.
[2] Nitzan, Z., US Patent 5,652,043.
[3] Cheng, F. et. al, Adv. Mater. 2005, 17, 2753-2756.
[4] Battery Reference Book, 3rd Edition, Crompton, T.R.

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