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Comparative capacity performance and electrochemical impedance spectroscopy of commercial AA alkaline primary cells
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Comparative capacity performance and electrochemical impedance spectroscopy of commercial AA alkaline primary cells E.E. Ferg ∗ , F. van Vuuren Department of Chemistry, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa
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Article history: Received 23 April 2013 Received in revised form 19 August 2013 Accepted 19 August 2013 Available online xxx Keywords: AA alkaline cells, Electrochemical impedance spectroscopy, Capacity performance
a b s t r a c t Alkaline primary cells are a relatively inexpensive source of portable power and there is still a significant demand for them due to their lower retail costs, good shelf life and good energy densities. There is a range of imported and local brands available in South Africa that can differ in terms of their cost to the consumer and their performance. The study being reported here compared a range of seven different AA alkaline brands in terms of price and performance by discharging them using three different standard tests, namely at constant 250 mA current, motor/toy and photo-flash respectively. The study also used electrochemical impedance spectroscopy (EIS) to observe differences between the different cell brands at different stages of discharge during the different discharge test sequences. The results showed that all cell brands achieved similar discharge capacities for the low-power discharge test of around 1.7 Ah at a constant current of 250 mA with significant differences in their respective purchase prices. However, significantly better discharge capacities of around 1.4 Ah were achieved for the more expensive brands for the photo-flash test when compared to the cheaper brand, where only 0.4 Ah was achieved. Hence, one can get value for money by using cheaper brand cells for typical low-power applications such as digital clocks, while the more expensive brands are recommended for high-power applications. The results of the EIS analysis showed that the internal cell resistance of the cheaper branded cells was relatively higher when compared to the more expensive branded cells. The change in the cheaper cells’ internal resistance was also comparatively higher when measured during the various stages of the discharge tests, especially during the photo-flash test. The EIS analysis also showed that certain new cells displayed an unusually high electrode capacitance and resistance when compared to the other cell types. This phenomenon then disappeared once the cells were slightly discharged to 1% of their respective capacities. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction Alkaline primary cells are a relatively inexpensive source of portable energy used in day-to-day applications such as electronic toys, torches, portable radios, cameras and digital clocks. Even though modern energy storage technologies have moved in the direction of rechargeable secondary-type cells that include the nickel metal hydride and the lithium-ion type chemistries, there is still a significant demand for alkaline primary cells that are comparatively cheaper to the modern rechargeable cells, have a good shelf life and good power or energy densities. The traditional alkaline cell chemistry was first developed around 1900 by Waledemar Junger and independently by Thomas Edison. However, the alkaline cell became commercial only in the 1960s [1,2]. Today, the Zn/MnO2 alkaline cell is available in a range
∗ Corresponding author. Tel.: +27 415043160. E-mail address: [email protected] (E.E. Ferg).
of sizes from coin- or button-type cells, to cylindrical cells and the lantern 6 V and 9 V square batteries that are usually specified by the International Electrotechnical Commission (IEC) in terms of size, shape and performance [3]. A typical AA alkaline cell is made up of a stainless steel outer canister, which is open on one side. The active MnO2 cathode material consists mainly of electrochemically made MnO2 (EMD). This type of MnO2 is more costly but of a higher purity with regular crystallite sizes and structure when compared to the natural MnO2 (NMD) or chemically pure MnO2 (CMD). Pellets of the active MnO2 are mixed with graphite and are pressed and inserted into the canister. The cathode is separated by a semi-permeable membrane from the anode that is made of pure zinc powder. The zinc powder is usually contained by a binder or gel that allows for ease of manufacturing. A metal rod is usually placed in the middle of the zinc powder that leads to the negative terminal of the battery housing. An aqueous 9 M KOH solution is used as the electrolyte [1,4]. The half-cell and overall discharge reactions for the Zn/MnO2 alkaline cell are well described by a number of authors as relatively complex
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with a number of intermediate products [5,6]. In simple terms, the discharge reactions at the cathode and anode can be described as follows: Anode : Cathode : Overall :
Zn(s) + 2OH− (aq) → ZnO(s) + H2 O(l) + 2e− 2MnO2 (s) ± H2 O(l) ± 2e− → Mn2 O3 (s) ± 2OH− (aq) Zn(s) + 2MnO2 (s) → ZnO(s) + Mn2 O3 (s)
The cost of manufacturing the Zn/MnO2 alkaline cell is relatively low as most of the process is fully automated. The primary raw materials of zinc and manganese and the aqueous hydroxide electrolyte are cheaper and more abundant when compared to materials used in other types of energy storage cells that contain cobalt, nickel and the rare-earth minerals that are used in metal hydrides and which, in the case of the lithium-ion cells, require the use of an organic-based electrolyte. In South Africa, as in many other countries, there is a range of imported brands available that can significantly differ in terms of their cost to the consumer and possibly their performance. It was of interest to compare a range of different AA alkaline cell brands by price and performance. The standard IEC specification tests are lengthy and the expected capacity for a particular application is often not indicated on the packaging of the brand. It was also of interest to observe whether there were any noticeable differences between the different cell types when subjected to a relatively versatile analytical technique known as electrochemical impedance spectroscopy (EIS). The analytical method of EIS is extensively used in the study of electrochemical cells that range from sensors to corrosion and energy storage cells [7–11]. Some EIS studies on alkaline cells that were usually configured in such a way as to allow for a reference electrode to be part of the cell make-up within the laboratory have been reported in the literature [12,13]. In evaluating an alkaline cell across the two electrode points only, the reference electrode is usually connected to the anode side of the cell. The resulting spectra are then a combination of the entire cell chemistry and one cannot always differentiate clearly between the various components such as the anode, cathode and electrolyte interface. The technique allows for the resulting spectra to be described by an equivalent circuit model that is made up of different components [8]. The most common technique used to describe energy storage cells is the Randel’s model for a single electrode and two electrode systems that are made up of a resistor and capacitor components in parallel. Over a frequency range, the spectra can be graphically displayed as a Nyquist plot where regions in the resulting spectra can be described by a suitable equivalent circuit model (Fig. 1). The equivalent circuit components can be described as Rint , the cells’ internal resistance, where the spectrum of the plot intersects the Z real axis. Rint is made up of the resistance that comes from the current collectors, electrolyte and separator material. The semicircle region of the spectrum would be the sum of the two electrode components in the cell and usually consists of a resistor and capacitor in parallel (regions 1 and 2 in Fig. 1). In some battery types, this region would be shown by two distinctive semi-circles; however, in the sealed AA alkaline cells these two regions overlapped. In the equivalent circuit model used in this study, a constant phase element (CPE) was used () instead of a straight capacitor [14]. The capacitance can be determined by knowing the exponent alpha (a), the CPE and the resistor value in parallel. In this case, a CPE model was used since the observed semi-circle was not truly symmetrical but formed mostly as an arc. Using the CPE in this study, the fitted equivalent circuit model gave an exponent (a) value of just less than one. This accommodated the electrodes’ surface roughness and porosity where in-homogenous reactions could take place that
Fig. 1. A typical Nyquist plot of an AA alkaline cell that was discharged to 1% of its capacity.
would result in a non-uniform current distribution. The straight line region that was at about 45◦ from the x-axis at the lower frequencies is known as the Warburg element. This is the region that describes the diffusion process in the active material when scanned at low frequencies. In simple terms, it describes the distance the diffusing reactants travel in the active material and is indicative of the diffusion-limited reactions that occur in the cell’s chemistry. The circuit also has an inductive region (L) that is the contribution due to the cell’s metallic components and sampling leads. 2. Experimental The AA alkaline cells chosen for the study were obtained from a number of large retail stores selling most common brands at similar prices. The purchase prices per cell were in South African rand (R) for a pack of four cells. Specials or bulk discount for the certain brand types were not considered and the seven cells chosen varied in their retail price and brand popularity. For this study, the results are reported in $ per cell by considering an exchange rate of 1 $ = 10 R respectively. 2.1. Cell capacity Short brass-rods with electrical ring connectors were soldered onto the cell electrode terminals ensuring good electrical contact. This allowed the cells to be firmly connected to the discharge testing equipment and impedance analyser. New AA cells in triplicate from each brand were subjected to the three discharge-type tests that were done on an MCV 16-10/1/0.1-12 bitrode battery tester according to IEC specifications [3]. The IEC 60086-2 tests were the motor/toy discharge, photo-flash discharge and a constant current discharge respectively. They are described in more detail as follows: 2.1.1. Constant current discharge The cells were subjected to continuous 250 mA constant current discharge until 0.9 V was reached. The total discharge capacity was recorded per cell. 2.1.2. Motor/toy discharge The cells were discharged at 3.9 constant resistance for 1 h/day followed by a 23-h open-circuit rest period. This was repeated until the voltage on discharge reached 0.9 V per cell. The accumulative cell capacity (Ah) was recorded over the number of discharge steps achieved.
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Fig. 2. Photo-flash discharge profile of a typical AA alkaline cell over seven respective cycles.
2.1.3. Photo-flash discharge The cells were discharged at 1000 mA for 10 s of every minute for an hour, followed by a 23-h open-circuit rest period. This was repeated until the voltage on discharge reached 0.9 V per cell. The accumulative cell capacity (Ah) was recorded over the number of discharge steps achieved. A typical photo-flash discharge profile done at room temperature for the AA alkaline cell is shown in Fig. 2. 2.2. Electrochemical impedance spectroscopy (EIS) EIS analysis was done on a set of new, fully charged cells before each of the discharge capacity tests was performed. With respect to the motor/toy and photo flash tests, EIS analysis was also done during the 23-h rest periods approximately 2 h after completing the preceding discharge step. Once the 250 mA constant current discharge tests had been done to determine the average capacity of the particular cell type, a new cell was discharged at 1%, 25%, 50%, 75% and 100% depth of discharge (DoD) of the initial average capacity. At each of the intervals, the cells were allowed to rest in open circuit for 2 h to allow the battery chemistry to equilibrate before commencing with an EIS analysis. The EIS analysis was done on a Gamry Reference 3000 in galvanostatic mode. The analysis was done between 30 kHz and 0.1 Hz with an AC current of 0.005 A rms with a 10-point/decade sampling interval. The DC current was set at 0 A. The working electrode connections were connected to the positive terminal and the counter electrode and the reference electrode connections were connected to the negative terminal of the cell. The equivalent circuit model of a two-cell design described in Fig. 1 was used to analyse the resulting data. 2.3. Material mass utilisation analysis Fully charged cells from each type were analysed for their active material content. The disassembling of the cells and the active mass of Zn and MnO2 were determined individually. Care was taken at the negative terminal not to short-circuit the cell since most of the brands had only a separator where the positive case was crimped over the negative terminal. The MnO2 was removed and rinsed over an ash-less Whatman 540 filter paper. The material was rinsed a few times with distilled water in order to remove the entire electrolyte. This was followed by placing the sample into a pre-weighed crucible and burning
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Fig. 3. Comparison of the achieved capacity for the different discharge tests and the cost per cell in $.
off the carbon additive at 700 ◦ C for 6 h. The complete removal of the carbon from the cathode active material was confirmed by TGA analysis where a small sample was analysed by heating it to 800 ◦ C and noting that no additional weight loss was observed above 700 ◦ C. From this, the active material mass of MnO2 for each of the cell type was determined. Similarly, the mass of the cells’ zinc powder was determined by rinsing the material through a pre-weighted filter paper. The sample was oven-dried overnight at 50 ◦ C. This was done in triplicate and the average active material mass was recorded. 3. Results and discussion For ease of discussion, the seven different AA alkaline cells were labelled from A to G. 3.1. Cost, capacity and material utilisation The range of AA cells chosen in terms of their purchasing price and their accumulative discharge capacities for the three tests is shown in Table 1. Fig. 3 shows the achieved discharge capacities of the cells for the different test methods against their respective cost in dollars ($). The results showed that on average, when comparing the discharge capacities for the different cell types, the results from the two low-power discharge tests (motor/toy and 250 mA) were similar in capacity (Ah) for the cells over the range of different cell prices. Significant differences of the discharge capacities were, however, achieved for the photo-flash test. The “cheaper” cells performed significantly poorer in total accumulative capacity when compared to the more expensive cell types. When the results of the discharge capacities per $ for each of the discharge tests were compared for the different cell types, some showed a significantly better capacity per $ value for the low-power discharge tests (B, D and G in Fig. 4). However, there was a considerable decrease in capacity per $ value for these cells when subjected to the high-power photo-flash test. The comparatively more expensive cells achieved similar capacities per $ value for the various discharge tests (cells A and F in Fig. 4). Comparatively, the cheaper cells achieve almost twice the capacity per $ value for the low-power discharge tests when compared to the more expensive cells. This implied that they are good value for money for typical applications such as toys, radios and digital clocks. However, for their use in high-power applications
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4 Table 1 Prices and capacities of the different battery brands. Capacity/Ah Battery brand A B C D E F G
Cost/$ 1.00 0.50 0.79 0.42 0.67 1.03 0.50
Motor/toy discharge test 1.953 1.832 2.133 1.876 1.995 1.843 1.813
Photo-flash discharge test 1.450 1.287 1.492 0.374 1.112 1.414 0.810
Constant 250 mA discharge test 1.779 1.748 1.856 1.765 1.656 1.562 1.613
Fig. 5. Overlay of the EIS Nyquist plots for all the new, fully charged alkaline cell brands. Fig. 4. A comparison of the different discharge capacities per $, achieved for the AA alkaline cells discharged at different rates.
3.2. EIS results
such photo-flash or portable high-power tools, their capacity performances are then significantly lower. It was important to determine the amount of active material used in the cells by the various manufacturers. The amount of active material used in the cell is usually the first measure of the possible achievable capacity and an indication of which electrode would be the limiting component in the capacity of an energy storage device. In the current study, all the cells had an excess amount of the anode Zn material when compared to the cathode. Hence, the theoretical capacity utilisation of the cells could be determined against the amount of MnO2 present, which is theoretically determined to be 308.3 mAh g−1 . The capacity utilisation for each of the different discharge types was then determined with respect to the theoretical MnO2 expected capacity (Table 2). Notably, the cell types B and F had on average slightly less active MnO2 material when compared to the other cells. Similar to the results in Fig. 4, the more expensive cells showed a better material utilisation for the photo flash test. However, for the motor/toy and 250 mA discharge tests, the material utilisation for the different cell brands was comparatively similar. The results showed that up to 68% of the active MnO2 material in the 250 mA discharge test was utilised. Even though cells B and F showed to contain slightly less active MnO2 material when compared to the others, their discharge capacities were comparatively similar for the 250 mA discharge test. This also implied that there might possibly be other factors that contribute to the lower discharge capacities for the photo flash test for cells D and G. These factors could include variations in particle surface area, porosity, types of graphite used and the separator material.
The overlaid EIS Nyquist plots of all the different new, fully charged cells are shown in Fig. 5. The analysis was repeated a few times and showed the same unusual anomaly for some of the cell brands. Three of the cells (E, F and G) showed Nyquist plots with a large semi-circle and cell G showed a slight looping backing at lower frequencies that might have been due to adsorption processes occurring at the electrode surfaces and possible thermal changes. This could be ascribed to larger than normal internal electrode resistances and cell-interface capacitance. By comparison to the in-lay graph in Fig. 5, the Nyquist plots of the other cells showed much smaller semi-circles with a tailing at the lower frequencies due to the typical Warburg impendence effect. The cells were all subsequently discharged to 1% depth of discharge (DoD) of their respective full capacity at the 250 mA discharge rate. Notably, the large semi-circles for the particular cells on the Nyquist plots disappeared (Fig. 6). Hence, this effect was only observed with new, fully charged cells and when discharged to 1% DoD, all the cell types showed similar EIS characteristics. EIS spectra were obtained at various intervals for the different discharge tests. As mentioned previously, the spectra during the motor/toy and photo-flash tests were done 2 h after the preceding discharge step. With regard to the 250 mA discharge tests, the cells were discharged to 1%, 25%, 50%, 75% and 100% DoD respectively, after which the cells were allowed to rest in open circuit for 2 h before EIS analysis. Analysing the EIS spectra at the various discharge stages was done by using the equivalent circuit model described in Fig. 1. A number of trends were observed between the various cell types, their discharge conditions and certain components used in the equivalent circuit model. The Rint that was associated with the internal resistance of the cell chemistry showed good correlations with the DoD of the various cells that were discharged by the three different test methods (Figs. 7–9).
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Table 2 Active material content and capacity utilisation for each of the different cell brands studied. Capacity (mAh g−1 ) Battery brand A B C D E F G
Mass of MnO2 (g) 9.269 8.279 8.924 8.824 9.273 8.407 8.641
Mole ratio of MnO2 /Zn 1.600 1.597 1.469 1.509 1.524 1.337 1.566
Motor/Toy discharge test 210.6 221.3 239.0 212.6 215.1 219.2 209.8
Material utilisation (%) Photo-flash discharge test 156.4 155.4 167.1 42.4 119.9 168.2 93.7
Fig. 6. Overlay of the EIS Nyquist plots for all the alkaline cell brands that were discharged to 1% DoD at 250 mA.
250 mA discharge test 191.9 211.2 207.9 200.0 178.6 185.8 186.7
Motor/Toy discharge test 68.3 71.8 77.5 69.0 69.8 71.1 68.1
Photo-flash discharge test 50.7 50.4 54.2 13.7 38.9 54.6 30.4
250 mA discharge test 62.3 68.5 67.5 64.9 57.9 60.3 60.6
Fig. 8. Change in the Rint parameter with discharge capacity for the alkaline cells discharged by the motor/toy discharge test.
The results showed that for all three types of discharge tests, the more expensive cells (F and A) correspondingly showed a slightly lower change in internal resistance during the discharge process. These cells also showed a better photo-flash total capacity performance. Notably, the cheaper cells (D and G) that also showed a relatively poor photo-flash performance showed a relatively higher initial Rint that increased significantly as the cells were discharged. Cell types B and E showed an intermediate change in the Rint with corresponding medium-performing photo-flash discharge abilities. The exception was for the cell type C that showed an average Rint
with a reasonably good photo-flash discharge capacity (Table 1). Hence, the results imply that the internal resistance contribution measured by EIS of the cell gave an indication of its performance during the high-current photo-flash discharge test. The factors that contribute to the internal resistance of a cell are often not due to one factor only. There might be contributions by the separator type used, the surface area of the electrode’s active material and the interface between the cell housing (current collector) and the active material [4].
Fig. 7. Change in the Rint parameter with discharge capacity for the alkaline cells discharged at 250 mA constant current.
Fig. 9. Change in the Rint parameter with discharge capacity for the alkaline cells discharged by the photo-flash discharge test.
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Fig. 10. Change in the R1 + R2 parameter with discharge capacity for the alkaline cells discharged by the motor/toy discharge test.
comparison, the change in (R1 + R2) with discharge for the photoflash discharge test is shown in Fig. 11 and shows that the higher comparative electrode resistances between the different cell brands did not directly influence the ability of the cell to achieve a high number of photo-flash discharge capacities. Notably, for cell type D, the (R1 + R2) parameter was reasonably low during the discharge test but showed a significant increase in the Rint value during the discharge, supporting the fact that the Rint is one of the main reasons for a lower high-power discharge ability for the type of test. The results further showed that the change in (R1 + R2) is slightly less for the photo-flash test when compared to the slower discharge test in the motor/toy test. This relates to the material utilisation, where the low-power discharge test used more of the active material, thereby showing a larger (R1 + R2) increase towards the end of the discharge when compared to the material utilisation of a cell that is subjected to a high power discharge test. The results also showed that cells E, F and G had a significantly higher (R1 + R2) at the beginning of the discharge test and that it decreased significantly after the first discharge test as shown in the Nyquist plots in Figs. 5 and 6 respectively. This relates to the unusual anomaly for three of the new cell types that subsequently disappeared after the first discharge step as discussed previously.
4. Conclusions
Fig. 11. Change in the R1 + R2 parameter with discharge capacity for the alkaline cells discharged by the photo-flash discharge test.
Possible trends for the other components in the equivalent circuit model used, such as the electrode capacitance and Warburg function for various cell types subjected to the three discharge tests, were not clearly observed. This is mainly due to the fact that accurate de-convolution of the single semi-circle in the Nyquist plot into each individual electrode contribution was not possible. This is usually achieved by using a suitable reference electrode that would be inserted into the active working cell, allowing for the EIS measurements to be done with respect to one of the working electrodes only. The inductance (L) results of the various cells studied were similar in value and relatively low that ranged between 66 × 10−9 H and 90 × 10−9 H. When considering the sum of the two electrode resistance components (R1 + R2) used in the equivalent circuit model, an increase in resistance value can be observed as the cells were discharged. The two resistance components of the two electrodes would, in simple terms, be the diameter of the semi-circle and should reflect an increase in its diameter as the cell is discharged and the active materials on the two electrodes becomes depleted. This is shown in Fig. 10, depicting the change in the sum of the two electrode resistance components (R1 + R2) from the EIS spectra of the various cells that were discharged by using the motor/toy test. For
The study showed that the saying, “something more expensive is better”, is not always true when it comes to AA alkaline cells that are used in low-current discharge applications, and that there is a significant value in terms of Ah/$ for the comparatively cheaper cell brands. However, the study also showed that the more expensive cell types would be better suited for high-power applications such as a photo-flash discharge. The reason for this could relate to the materials used in the cell manufacturing. The study showed that the material utilisation of the MnO2 was significantly high (71%) for the low-power motor/toy application across the various cell types. The fact that there was a significant difference between the high-power applications suggests that an improvement in material utilisation was not necessarily the case for the cheaper cells in order to achieve comparable high-power capacities. The extra high-power achievable for the application that was obtained from the more expensive cells probably relates to some cell design feature that is more expensive, thereby making the retail cell price of the cells higher. The EIS analysis of these cells suggested that Rint plays a significant role in achieving significant high-power capacity. This can relate to a number of contributions that might include extra conductive additives and separator design. Johansen in his PhD dissertation on the modelling of the discharge of alkaline cells suggested that the porous separator and its interaction with the discharge material at the anode could have a significant influence on the achievable capacity [4]. Also, manufacturers could apply techniques that include the use of various types of conductive coatings to improve the conductivity between the current collector (cell housing) and the active electrode material. The current study showed that EIS is a well-suited technique to evaluate the electrochemistry of sealed AA alkaline cells. Even though full de-convoluted spectra for the electrode contributions could not be achieved, and although there are many complex factors in the discharge reactions of the active material that can make the modelling relatively complex, valuable information is available in terms of the internal cell resistance that relate to its high-power discharge ability. The study showed that a cell with a higher internal resistance (Rint ) would not perform well in high-power applications when compared to a cell with a lower Rint . The unusual phenomenon of large semi-circles in the Nyquist plots for some of the cells also showed that some manufacturers “tweak” their cells
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electrochemically in some way in order to improve the cells’ performance in terms of shelf life or initial discharge capacity. Hence, one can then say that, even though all the alkaline cells in the current study presented similar capacity performance in typical low-power applications, they are “not all made equal”. Acknowledgement The authors thank Seetharaman Srinivasan from Eveready Batteries South Africa for valuable discussion and supplying some of the cell types used in this study. References [1] D. Linden, Handbook of Batteries 3rd Edition., McGraw-Hill, New York, 2002. [2] P.A. Marsal, K.Kordesch and L.F.Urry., Dry Cell, U.C. Corp,;1; USA Patent 2960558, 1960. [3] International Electrotechnical Commission, Primary batteries 11th Ed, Part 2: Physical and electrical specifications, Geneva, Switzerland, 2006. [4] J. Johansen. Mathematical Modelling of Primary Alkaline Batteries. PhD Thesis. Queensland University of Technology. Brisbane. 2007.
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[5] N.C. Cahoon, M.P. Korver, The cathodic reduction of manganese dioxide in alkaline electrolyte, J. Electrochem. Soc. 106 (9) (1959) 745. [6] Y. Chabre, J. Pannetier, Structural and electrochemical properties of the proton/␥MnO2 system, Prog. Solid State Chem. 23 (1) (1995) 1. [7] D. Depernet, O. Ba, A. Berthon, Online impedance spectroscopy of lead acid batteries for storage management of a standalone power plant, J. Power Sources 219 (0) (2012) 65. [8] Garmy Instruments, Application notes: Basics of Electrochemical Impedance Spectroscopy, Pennsylvania, USA, 2010. [9] E. Karden, S. Buller, R.W. De Doncker, A method for measurement and interpretation of impedance spectra for industrial batteries, J. Power Sources 85 (1) (2000) 72. [10] M.E. Orazem, B. Tribollet, An integrated approach to electrochemical impedance spectroscopy, Electrochim. Acta 53 (25) (2008) 7360. [11] M. Thele, O. Bohlen, D.U. Sauer, E. Karden, Development of a voltage-behaviour model for NiMH batteries using an impedance-based modelling concept, J. Power Sources 175 (1) (2008) 635. [12] J.B. Arnott, G.J. Browning, S.W. Donne, Study on manganese dioxide discharge using electrochemical impedance spectroscopy, J. Electrochem. Soc. 153 (7) (2006) A1332. [13] S.W. Done, J.H. Kennedy, Electrochemical impedance spectroscopy of the alkaline manganese dioxide electrode, J. Appl. Electrochem. 34 (2) (2004) 159. [14] E. Barsoukov, J.R. Macdonald, Impedance spectroscopy theory, in: Experiment and Applications, 2nd Ed., John Wiley and Sons, New Jersey, USA, 2005.
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Comparative capacity performance and electrochemical impedance spectroscopy of commercial AA alkaline primary cells E.E. Ferg ∗ , F. van Vuuren Department of Chemistry, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa
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Article history: Received 23 April 2013 Received in revised form 19 August 2013 Accepted 19 August 2013 Available online xxx Keywords: AA alkaline cells, Electrochemical impedance spectroscopy, Capacity performance
a b s t r a c t Alkaline primary cells are a relatively inexpensive source of portable power and there is still a significant demand for them due to their lower retail costs, good shelf life and good energy densities. There is a range of imported and local brands available in South Africa that can differ in terms of their cost to the consumer and their performance. The study being reported here compared a range of seven different AA alkaline brands in terms of price and performance by discharging them using three different standard tests, namely at constant 250 mA current, motor/toy and photo-flash respectively. The study also used electrochemical impedance spectroscopy (EIS) to observe differences between the different cell brands at different stages of discharge during the different discharge test sequences. The results showed that all cell brands achieved similar discharge capacities for the low-power discharge test of around 1.7 Ah at a constant current of 250 mA with significant differences in their respective purchase prices. However, significantly better discharge capacities of around 1.4 Ah were achieved for the more expensive brands for the photo-flash test when compared to the cheaper brand, where only 0.4 Ah was achieved. Hence, one can get value for money by using cheaper brand cells for typical low-power applications such as digital clocks, while the more expensive brands are recommended for high-power applications. The results of the EIS analysis showed that the internal cell resistance of the cheaper branded cells was relatively higher when compared to the more expensive branded cells. The change in the cheaper cells’ internal resistance was also comparatively higher when measured during the various stages of the discharge tests, especially during the photo-flash test. The EIS analysis also showed that certain new cells displayed an unusually high electrode capacitance and resistance when compared to the other cell types. This phenomenon then disappeared once the cells were slightly discharged to 1% of their respective capacities. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction Alkaline primary cells are a relatively inexpensive source of portable energy used in day-to-day applications such as electronic toys, torches, portable radios, cameras and digital clocks. Even though modern energy storage technologies have moved in the direction of rechargeable secondary-type cells that include the nickel metal hydride and the lithium-ion type chemistries, there is still a significant demand for alkaline primary cells that are comparatively cheaper to the modern rechargeable cells, have a good shelf life and good power or energy densities. The traditional alkaline cell chemistry was first developed around 1900 by Waledemar Junger and independently by Thomas Edison. However, the alkaline cell became commercial only in the 1960s [1,2]. Today, the Zn/MnO2 alkaline cell is available in a range
∗ Corresponding author. Tel.: +27 415043160. E-mail address: [email protected] (E.E. Ferg).
of sizes from coin- or button-type cells, to cylindrical cells and the lantern 6 V and 9 V square batteries that are usually specified by the International Electrotechnical Commission (IEC) in terms of size, shape and performance [3]. A typical AA alkaline cell is made up of a stainless steel outer canister, which is open on one side. The active MnO2 cathode material consists mainly of electrochemically made MnO2 (EMD). This type of MnO2 is more costly but of a higher purity with regular crystallite sizes and structure when compared to the natural MnO2 (NMD) or chemically pure MnO2 (CMD). Pellets of the active MnO2 are mixed with graphite and are pressed and inserted into the canister. The cathode is separated by a semi-permeable membrane from the anode that is made of pure zinc powder. The zinc powder is usually contained by a binder or gel that allows for ease of manufacturing. A metal rod is usually placed in the middle of the zinc powder that leads to the negative terminal of the battery housing. An aqueous 9 M KOH solution is used as the electrolyte [1,4]. The half-cell and overall discharge reactions for the Zn/MnO2 alkaline cell are well described by a number of authors as relatively complex
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with a number of intermediate products [5,6]. In simple terms, the discharge reactions at the cathode and anode can be described as follows: Anode : Cathode : Overall :
Zn(s) + 2OH− (aq) → ZnO(s) + H2 O(l) + 2e− 2MnO2 (s) ± H2 O(l) ± 2e− → Mn2 O3 (s) ± 2OH− (aq) Zn(s) + 2MnO2 (s) → ZnO(s) + Mn2 O3 (s)
The cost of manufacturing the Zn/MnO2 alkaline cell is relatively low as most of the process is fully automated. The primary raw materials of zinc and manganese and the aqueous hydroxide electrolyte are cheaper and more abundant when compared to materials used in other types of energy storage cells that contain cobalt, nickel and the rare-earth minerals that are used in metal hydrides and which, in the case of the lithium-ion cells, require the use of an organic-based electrolyte. In South Africa, as in many other countries, there is a range of imported brands available that can significantly differ in terms of their cost to the consumer and possibly their performance. It was of interest to compare a range of different AA alkaline cell brands by price and performance. The standard IEC specification tests are lengthy and the expected capacity for a particular application is often not indicated on the packaging of the brand. It was also of interest to observe whether there were any noticeable differences between the different cell types when subjected to a relatively versatile analytical technique known as electrochemical impedance spectroscopy (EIS). The analytical method of EIS is extensively used in the study of electrochemical cells that range from sensors to corrosion and energy storage cells [7–11]. Some EIS studies on alkaline cells that were usually configured in such a way as to allow for a reference electrode to be part of the cell make-up within the laboratory have been reported in the literature [12,13]. In evaluating an alkaline cell across the two electrode points only, the reference electrode is usually connected to the anode side of the cell. The resulting spectra are then a combination of the entire cell chemistry and one cannot always differentiate clearly between the various components such as the anode, cathode and electrolyte interface. The technique allows for the resulting spectra to be described by an equivalent circuit model that is made up of different components [8]. The most common technique used to describe energy storage cells is the Randel’s model for a single electrode and two electrode systems that are made up of a resistor and capacitor components in parallel. Over a frequency range, the spectra can be graphically displayed as a Nyquist plot where regions in the resulting spectra can be described by a suitable equivalent circuit model (Fig. 1). The equivalent circuit components can be described as Rint , the cells’ internal resistance, where the spectrum of the plot intersects the Z real axis. Rint is made up of the resistance that comes from the current collectors, electrolyte and separator material. The semicircle region of the spectrum would be the sum of the two electrode components in the cell and usually consists of a resistor and capacitor in parallel (regions 1 and 2 in Fig. 1). In some battery types, this region would be shown by two distinctive semi-circles; however, in the sealed AA alkaline cells these two regions overlapped. In the equivalent circuit model used in this study, a constant phase element (CPE) was used () instead of a straight capacitor [14]. The capacitance can be determined by knowing the exponent alpha (a), the CPE and the resistor value in parallel. In this case, a CPE model was used since the observed semi-circle was not truly symmetrical but formed mostly as an arc. Using the CPE in this study, the fitted equivalent circuit model gave an exponent (a) value of just less than one. This accommodated the electrodes’ surface roughness and porosity where in-homogenous reactions could take place that
Fig. 1. A typical Nyquist plot of an AA alkaline cell that was discharged to 1% of its capacity.
would result in a non-uniform current distribution. The straight line region that was at about 45◦ from the x-axis at the lower frequencies is known as the Warburg element. This is the region that describes the diffusion process in the active material when scanned at low frequencies. In simple terms, it describes the distance the diffusing reactants travel in the active material and is indicative of the diffusion-limited reactions that occur in the cell’s chemistry. The circuit also has an inductive region (L) that is the contribution due to the cell’s metallic components and sampling leads. 2. Experimental The AA alkaline cells chosen for the study were obtained from a number of large retail stores selling most common brands at similar prices. The purchase prices per cell were in South African rand (R) for a pack of four cells. Specials or bulk discount for the certain brand types were not considered and the seven cells chosen varied in their retail price and brand popularity. For this study, the results are reported in $ per cell by considering an exchange rate of 1 $ = 10 R respectively. 2.1. Cell capacity Short brass-rods with electrical ring connectors were soldered onto the cell electrode terminals ensuring good electrical contact. This allowed the cells to be firmly connected to the discharge testing equipment and impedance analyser. New AA cells in triplicate from each brand were subjected to the three discharge-type tests that were done on an MCV 16-10/1/0.1-12 bitrode battery tester according to IEC specifications [3]. The IEC 60086-2 tests were the motor/toy discharge, photo-flash discharge and a constant current discharge respectively. They are described in more detail as follows: 2.1.1. Constant current discharge The cells were subjected to continuous 250 mA constant current discharge until 0.9 V was reached. The total discharge capacity was recorded per cell. 2.1.2. Motor/toy discharge The cells were discharged at 3.9 constant resistance for 1 h/day followed by a 23-h open-circuit rest period. This was repeated until the voltage on discharge reached 0.9 V per cell. The accumulative cell capacity (Ah) was recorded over the number of discharge steps achieved.
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Fig. 2. Photo-flash discharge profile of a typical AA alkaline cell over seven respective cycles.
2.1.3. Photo-flash discharge The cells were discharged at 1000 mA for 10 s of every minute for an hour, followed by a 23-h open-circuit rest period. This was repeated until the voltage on discharge reached 0.9 V per cell. The accumulative cell capacity (Ah) was recorded over the number of discharge steps achieved. A typical photo-flash discharge profile done at room temperature for the AA alkaline cell is shown in Fig. 2. 2.2. Electrochemical impedance spectroscopy (EIS) EIS analysis was done on a set of new, fully charged cells before each of the discharge capacity tests was performed. With respect to the motor/toy and photo flash tests, EIS analysis was also done during the 23-h rest periods approximately 2 h after completing the preceding discharge step. Once the 250 mA constant current discharge tests had been done to determine the average capacity of the particular cell type, a new cell was discharged at 1%, 25%, 50%, 75% and 100% depth of discharge (DoD) of the initial average capacity. At each of the intervals, the cells were allowed to rest in open circuit for 2 h to allow the battery chemistry to equilibrate before commencing with an EIS analysis. The EIS analysis was done on a Gamry Reference 3000 in galvanostatic mode. The analysis was done between 30 kHz and 0.1 Hz with an AC current of 0.005 A rms with a 10-point/decade sampling interval. The DC current was set at 0 A. The working electrode connections were connected to the positive terminal and the counter electrode and the reference electrode connections were connected to the negative terminal of the cell. The equivalent circuit model of a two-cell design described in Fig. 1 was used to analyse the resulting data. 2.3. Material mass utilisation analysis Fully charged cells from each type were analysed for their active material content. The disassembling of the cells and the active mass of Zn and MnO2 were determined individually. Care was taken at the negative terminal not to short-circuit the cell since most of the brands had only a separator where the positive case was crimped over the negative terminal. The MnO2 was removed and rinsed over an ash-less Whatman 540 filter paper. The material was rinsed a few times with distilled water in order to remove the entire electrolyte. This was followed by placing the sample into a pre-weighed crucible and burning
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Fig. 3. Comparison of the achieved capacity for the different discharge tests and the cost per cell in $.
off the carbon additive at 700 ◦ C for 6 h. The complete removal of the carbon from the cathode active material was confirmed by TGA analysis where a small sample was analysed by heating it to 800 ◦ C and noting that no additional weight loss was observed above 700 ◦ C. From this, the active material mass of MnO2 for each of the cell type was determined. Similarly, the mass of the cells’ zinc powder was determined by rinsing the material through a pre-weighted filter paper. The sample was oven-dried overnight at 50 ◦ C. This was done in triplicate and the average active material mass was recorded. 3. Results and discussion For ease of discussion, the seven different AA alkaline cells were labelled from A to G. 3.1. Cost, capacity and material utilisation The range of AA cells chosen in terms of their purchasing price and their accumulative discharge capacities for the three tests is shown in Table 1. Fig. 3 shows the achieved discharge capacities of the cells for the different test methods against their respective cost in dollars ($). The results showed that on average, when comparing the discharge capacities for the different cell types, the results from the two low-power discharge tests (motor/toy and 250 mA) were similar in capacity (Ah) for the cells over the range of different cell prices. Significant differences of the discharge capacities were, however, achieved for the photo-flash test. The “cheaper” cells performed significantly poorer in total accumulative capacity when compared to the more expensive cell types. When the results of the discharge capacities per $ for each of the discharge tests were compared for the different cell types, some showed a significantly better capacity per $ value for the low-power discharge tests (B, D and G in Fig. 4). However, there was a considerable decrease in capacity per $ value for these cells when subjected to the high-power photo-flash test. The comparatively more expensive cells achieved similar capacities per $ value for the various discharge tests (cells A and F in Fig. 4). Comparatively, the cheaper cells achieve almost twice the capacity per $ value for the low-power discharge tests when compared to the more expensive cells. This implied that they are good value for money for typical applications such as toys, radios and digital clocks. However, for their use in high-power applications
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4 Table 1 Prices and capacities of the different battery brands. Capacity/Ah Battery brand A B C D E F G
Cost/$ 1.00 0.50 0.79 0.42 0.67 1.03 0.50
Motor/toy discharge test 1.953 1.832 2.133 1.876 1.995 1.843 1.813
Photo-flash discharge test 1.450 1.287 1.492 0.374 1.112 1.414 0.810
Constant 250 mA discharge test 1.779 1.748 1.856 1.765 1.656 1.562 1.613
Fig. 5. Overlay of the EIS Nyquist plots for all the new, fully charged alkaline cell brands. Fig. 4. A comparison of the different discharge capacities per $, achieved for the AA alkaline cells discharged at different rates.
3.2. EIS results
such photo-flash or portable high-power tools, their capacity performances are then significantly lower. It was important to determine the amount of active material used in the cells by the various manufacturers. The amount of active material used in the cell is usually the first measure of the possible achievable capacity and an indication of which electrode would be the limiting component in the capacity of an energy storage device. In the current study, all the cells had an excess amount of the anode Zn material when compared to the cathode. Hence, the theoretical capacity utilisation of the cells could be determined against the amount of MnO2 present, which is theoretically determined to be 308.3 mAh g−1 . The capacity utilisation for each of the different discharge types was then determined with respect to the theoretical MnO2 expected capacity (Table 2). Notably, the cell types B and F had on average slightly less active MnO2 material when compared to the other cells. Similar to the results in Fig. 4, the more expensive cells showed a better material utilisation for the photo flash test. However, for the motor/toy and 250 mA discharge tests, the material utilisation for the different cell brands was comparatively similar. The results showed that up to 68% of the active MnO2 material in the 250 mA discharge test was utilised. Even though cells B and F showed to contain slightly less active MnO2 material when compared to the others, their discharge capacities were comparatively similar for the 250 mA discharge test. This also implied that there might possibly be other factors that contribute to the lower discharge capacities for the photo flash test for cells D and G. These factors could include variations in particle surface area, porosity, types of graphite used and the separator material.
The overlaid EIS Nyquist plots of all the different new, fully charged cells are shown in Fig. 5. The analysis was repeated a few times and showed the same unusual anomaly for some of the cell brands. Three of the cells (E, F and G) showed Nyquist plots with a large semi-circle and cell G showed a slight looping backing at lower frequencies that might have been due to adsorption processes occurring at the electrode surfaces and possible thermal changes. This could be ascribed to larger than normal internal electrode resistances and cell-interface capacitance. By comparison to the in-lay graph in Fig. 5, the Nyquist plots of the other cells showed much smaller semi-circles with a tailing at the lower frequencies due to the typical Warburg impendence effect. The cells were all subsequently discharged to 1% depth of discharge (DoD) of their respective full capacity at the 250 mA discharge rate. Notably, the large semi-circles for the particular cells on the Nyquist plots disappeared (Fig. 6). Hence, this effect was only observed with new, fully charged cells and when discharged to 1% DoD, all the cell types showed similar EIS characteristics. EIS spectra were obtained at various intervals for the different discharge tests. As mentioned previously, the spectra during the motor/toy and photo-flash tests were done 2 h after the preceding discharge step. With regard to the 250 mA discharge tests, the cells were discharged to 1%, 25%, 50%, 75% and 100% DoD respectively, after which the cells were allowed to rest in open circuit for 2 h before EIS analysis. Analysing the EIS spectra at the various discharge stages was done by using the equivalent circuit model described in Fig. 1. A number of trends were observed between the various cell types, their discharge conditions and certain components used in the equivalent circuit model. The Rint that was associated with the internal resistance of the cell chemistry showed good correlations with the DoD of the various cells that were discharged by the three different test methods (Figs. 7–9).
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Table 2 Active material content and capacity utilisation for each of the different cell brands studied. Capacity (mAh g−1 ) Battery brand A B C D E F G
Mass of MnO2 (g) 9.269 8.279 8.924 8.824 9.273 8.407 8.641
Mole ratio of MnO2 /Zn 1.600 1.597 1.469 1.509 1.524 1.337 1.566
Motor/Toy discharge test 210.6 221.3 239.0 212.6 215.1 219.2 209.8
Material utilisation (%) Photo-flash discharge test 156.4 155.4 167.1 42.4 119.9 168.2 93.7
Fig. 6. Overlay of the EIS Nyquist plots for all the alkaline cell brands that were discharged to 1% DoD at 250 mA.
250 mA discharge test 191.9 211.2 207.9 200.0 178.6 185.8 186.7
Motor/Toy discharge test 68.3 71.8 77.5 69.0 69.8 71.1 68.1
Photo-flash discharge test 50.7 50.4 54.2 13.7 38.9 54.6 30.4
250 mA discharge test 62.3 68.5 67.5 64.9 57.9 60.3 60.6
Fig. 8. Change in the Rint parameter with discharge capacity for the alkaline cells discharged by the motor/toy discharge test.
The results showed that for all three types of discharge tests, the more expensive cells (F and A) correspondingly showed a slightly lower change in internal resistance during the discharge process. These cells also showed a better photo-flash total capacity performance. Notably, the cheaper cells (D and G) that also showed a relatively poor photo-flash performance showed a relatively higher initial Rint that increased significantly as the cells were discharged. Cell types B and E showed an intermediate change in the Rint with corresponding medium-performing photo-flash discharge abilities. The exception was for the cell type C that showed an average Rint
with a reasonably good photo-flash discharge capacity (Table 1). Hence, the results imply that the internal resistance contribution measured by EIS of the cell gave an indication of its performance during the high-current photo-flash discharge test. The factors that contribute to the internal resistance of a cell are often not due to one factor only. There might be contributions by the separator type used, the surface area of the electrode’s active material and the interface between the cell housing (current collector) and the active material [4].
Fig. 7. Change in the Rint parameter with discharge capacity for the alkaline cells discharged at 250 mA constant current.
Fig. 9. Change in the Rint parameter with discharge capacity for the alkaline cells discharged by the photo-flash discharge test.
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Fig. 10. Change in the R1 + R2 parameter with discharge capacity for the alkaline cells discharged by the motor/toy discharge test.
comparison, the change in (R1 + R2) with discharge for the photoflash discharge test is shown in Fig. 11 and shows that the higher comparative electrode resistances between the different cell brands did not directly influence the ability of the cell to achieve a high number of photo-flash discharge capacities. Notably, for cell type D, the (R1 + R2) parameter was reasonably low during the discharge test but showed a significant increase in the Rint value during the discharge, supporting the fact that the Rint is one of the main reasons for a lower high-power discharge ability for the type of test. The results further showed that the change in (R1 + R2) is slightly less for the photo-flash test when compared to the slower discharge test in the motor/toy test. This relates to the material utilisation, where the low-power discharge test used more of the active material, thereby showing a larger (R1 + R2) increase towards the end of the discharge when compared to the material utilisation of a cell that is subjected to a high power discharge test. The results also showed that cells E, F and G had a significantly higher (R1 + R2) at the beginning of the discharge test and that it decreased significantly after the first discharge test as shown in the Nyquist plots in Figs. 5 and 6 respectively. This relates to the unusual anomaly for three of the new cell types that subsequently disappeared after the first discharge step as discussed previously.
4. Conclusions
Fig. 11. Change in the R1 + R2 parameter with discharge capacity for the alkaline cells discharged by the photo-flash discharge test.
Possible trends for the other components in the equivalent circuit model used, such as the electrode capacitance and Warburg function for various cell types subjected to the three discharge tests, were not clearly observed. This is mainly due to the fact that accurate de-convolution of the single semi-circle in the Nyquist plot into each individual electrode contribution was not possible. This is usually achieved by using a suitable reference electrode that would be inserted into the active working cell, allowing for the EIS measurements to be done with respect to one of the working electrodes only. The inductance (L) results of the various cells studied were similar in value and relatively low that ranged between 66 × 10−9 H and 90 × 10−9 H. When considering the sum of the two electrode resistance components (R1 + R2) used in the equivalent circuit model, an increase in resistance value can be observed as the cells were discharged. The two resistance components of the two electrodes would, in simple terms, be the diameter of the semi-circle and should reflect an increase in its diameter as the cell is discharged and the active materials on the two electrodes becomes depleted. This is shown in Fig. 10, depicting the change in the sum of the two electrode resistance components (R1 + R2) from the EIS spectra of the various cells that were discharged by using the motor/toy test. For
The study showed that the saying, “something more expensive is better”, is not always true when it comes to AA alkaline cells that are used in low-current discharge applications, and that there is a significant value in terms of Ah/$ for the comparatively cheaper cell brands. However, the study also showed that the more expensive cell types would be better suited for high-power applications such as a photo-flash discharge. The reason for this could relate to the materials used in the cell manufacturing. The study showed that the material utilisation of the MnO2 was significantly high (71%) for the low-power motor/toy application across the various cell types. The fact that there was a significant difference between the high-power applications suggests that an improvement in material utilisation was not necessarily the case for the cheaper cells in order to achieve comparable high-power capacities. The extra high-power achievable for the application that was obtained from the more expensive cells probably relates to some cell design feature that is more expensive, thereby making the retail cell price of the cells higher. The EIS analysis of these cells suggested that Rint plays a significant role in achieving significant high-power capacity. This can relate to a number of contributions that might include extra conductive additives and separator design. Johansen in his PhD dissertation on the modelling of the discharge of alkaline cells suggested that the porous separator and its interaction with the discharge material at the anode could have a significant influence on the achievable capacity [4]. Also, manufacturers could apply techniques that include the use of various types of conductive coatings to improve the conductivity between the current collector (cell housing) and the active electrode material. The current study showed that EIS is a well-suited technique to evaluate the electrochemistry of sealed AA alkaline cells. Even though full de-convoluted spectra for the electrode contributions could not be achieved, and although there are many complex factors in the discharge reactions of the active material that can make the modelling relatively complex, valuable information is available in terms of the internal cell resistance that relate to its high-power discharge ability. The study showed that a cell with a higher internal resistance (Rint ) would not perform well in high-power applications when compared to a cell with a lower Rint . The unusual phenomenon of large semi-circles in the Nyquist plots for some of the cells also showed that some manufacturers “tweak” their cells
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electrochemically in some way in order to improve the cells’ performance in terms of shelf life or initial discharge capacity. Hence, one can then say that, even though all the alkaline cells in the current study presented similar capacity performance in typical low-power applications, they are “not all made equal”. Acknowledgement The authors thank Seetharaman Srinivasan from Eveready Batteries South Africa for valuable discussion and supplying some of the cell types used in this study. References [1] D. Linden, Handbook of Batteries 3rd Edition., McGraw-Hill, New York, 2002. [2] P.A. Marsal, K.Kordesch and L.F.Urry., Dry Cell, U.C. Corp,;1; USA Patent 2960558, 1960. [3] International Electrotechnical Commission, Primary batteries 11th Ed, Part 2: Physical and electrical specifications, Geneva, Switzerland, 2006. [4] J. Johansen. Mathematical Modelling of Primary Alkaline Batteries. PhD Thesis. Queensland University of Technology. Brisbane. 2007.
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[5] N.C. Cahoon, M.P. Korver, The cathodic reduction of manganese dioxide in alkaline electrolyte, J. Electrochem. Soc. 106 (9) (1959) 745. [6] Y. Chabre, J. Pannetier, Structural and electrochemical properties of the proton/␥MnO2 system, Prog. Solid State Chem. 23 (1) (1995) 1. [7] D. Depernet, O. Ba, A. Berthon, Online impedance spectroscopy of lead acid batteries for storage management of a standalone power plant, J. Power Sources 219 (0) (2012) 65. [8] Garmy Instruments, Application notes: Basics of Electrochemical Impedance Spectroscopy, Pennsylvania, USA, 2010. [9] E. Karden, S. Buller, R.W. De Doncker, A method for measurement and interpretation of impedance spectra for industrial batteries, J. Power Sources 85 (1) (2000) 72. [10] M.E. Orazem, B. Tribollet, An integrated approach to electrochemical impedance spectroscopy, Electrochim. Acta 53 (25) (2008) 7360. [11] M. Thele, O. Bohlen, D.U. Sauer, E. Karden, Development of a voltage-behaviour model for NiMH batteries using an impedance-based modelling concept, J. Power Sources 175 (1) (2008) 635. [12] J.B. Arnott, G.J. Browning, S.W. Donne, Study on manganese dioxide discharge using electrochemical impedance spectroscopy, J. Electrochem. Soc. 153 (7) (2006) A1332. [13] S.W. Done, J.H. Kennedy, Electrochemical impedance spectroscopy of the alkaline manganese dioxide electrode, J. Appl. Electrochem. 34 (2) (2004) 159. [14] E. Barsoukov, J.R. Macdonald, Impedance spectroscopy theory, in: Experiment and Applications, 2nd Ed., John Wiley and Sons, New Jersey, USA, 2005.
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