COPPER OXIDES IN NEUTRAL SOLUTIONS

Nakayama, Kaji, Notoya, and Osakai (2002), Nakayama, Kaji, Shibata, Notoya, and Osakai (2007), Nakayama, Kaji, Notoya, and Osakai (2008), Nakayama (2009) have used E1S to study the mechanism of reduction of copper oxides in alkaline and neutral solutions. Copper and copper alloys are widely used in industrial fields for the manufacturing of electrical wires, electronic components, electrical materials, and many other products. Although copper is a relatively corrosion-resistant material, oxide films of various thicknesses are formed on copper, which are exposed to air containing moisture and pollutants. The oxide films on copper consist of copper oxide (Cu20) and/or copper oxide (CuO). The selective determination of two oxides with different properties is important for the characterization of corrosion. A CuO/Cu sample and a CuO/Cu20/Cu oxide film of a Cu-duplex of Cu20/Cu oxide were prepared.

Nyquist representation of the impedance given in Figure 3.24 for CPE exponent = 6.67. The marked impedance at a frequency of 2 x 1 O' Hz is close to characteristic frequency f- 1.8 x КГ Hz

FIGURE 3.23 Nyquist representation of the impedance given in Figure 3.24 for CPE exponent = 6.67. The marked impedance at a frequency of 2 x 1 O'5 Hz is close to characteristic frequency f0- 1.8 x КГ5 Hz.

A distribution of RC elements that corresponds to the impedance response of a film. Reproduced with permission from Hirschorn ct al. (2010). Copyright 2010, Electrochemical Society

FIGURE 3.24 A distribution of RC elements that corresponds to the impedance response of a film. Reproduced with permission from Hirschorn ct al. (2010). Copyright 2010, Electrochemical Society.

Using X-ray diffraction, it was shown that Cu20 and CuO coexist on the surface of the CuO/Cu20/Cu sample. The presence of a Cu20 or CuO film on Cu20/Cu and CuO/Cu samples was also found by X-ray diffraction. In electrochemical measurements for standard samples, the test surface area was 1.0 cnr. A Cu20, CuO, and Cu(OH)2 powder samples were mixed with carbon paste (BAS Inc.) before each measurement (Nakayama et al., 2004). The mass ratio of the powder sample to carbon paste was 1:5. The amplitude of the superimposed current modulation was 0.1 mA, and the frequency range was from 50 MHz to 10 kHz.

The electrochemical impedance for the reduction of CuO was not strongly dependent on the type of alkaline solutions (see Figures 3.25a). Instead, the electrochemical impedance for the reduction of Cu20 was significantly dependent on the type and concentration of

Electrochemical impedances of CuO/Cu (a) and СЧьО/Си (b) sample in 1 M LiOH. 1 M NaOH, and 1 M KOH (DC current

FIGURE 3.25 Electrochemical impedances of CuO/Cu (a) and СЧьО/Си (b) sample in 1 M LiOH. 1 M NaOH, and 1 M KOH (DC current: -1.0 mA; AC current: 0.1 mA).

Data adapted with permission from Nakavama et al., 2008. Copyright 2008, Elsevier.

alkali metal chloride (see Figures 3.25b and 3.26). Figure 3.26 shows Nyquist plot of Cu20/ Си samples in LiOH solutions of various concentrations.

The diameter of the capacitive loop, that is, the charge transfers resistance (Rcl), increased with increasing LiOH concentration, particularly in the region above 1 M. On the other hand, the specific behavior of the transient decrease in Rcl and the appearance of the inductive loop was confirmed when the LiOH concentration was higher than 0.5 M. A strongly alkaline solution containing Li ion is necessary for the simultaneous determination of Cu20, CuO, and Cu(OH)2 on the surface of copper. Moreover, Rcl again increases with an increase in LiOH concentration of more than 1 M. These dependences may correspond to a good separation between reduction potentials of CuO and Cu20 in chronopotentiometric measurements. However, the reduction potential of Cu(OH)2 has shifted to a lower direction in neutral decisions. A sufficient separation between the reduction potentials of Cu(OH)2 and Cu20 was difficult.

Nyquist plot of Cu0/Cu samples in KOH solutions of various concentrations (0.1 to 3 M). DC current

FIGURE 3.26 Nyquist plot of Cu20/Cu samples in KOH solutions of various concentrations (0.1 to 3 M). DC current: -1.0 mA, AC current: 0.1 mA.

Data adapted with permission from Nakayama et al., 2008. Copyright 2008, Elsevier.

LITHIUM NICKEL MANGANESE COBALT OXIDE POUCH CELLS

Lithium-ion batteries (LIBs) are becoming the main energy storage devices in the sectors of communication, transport, and renewable energy sources (Opitz, Badami, Shen, Vignaroo- ban, & Kannan, 2017). However, the maximum possible energy supply for the LIB is insufficient for the long-term needs of society, for example, for long-range electric vehicles, hybrid electric vehicles and other portable devices (Nykvist, & Nilsson. 2015). Currently, the trend for electric vehicles is increasing sharply, especially in developed countries, as carbon dioxide emissions are becoming a serious problem in this decade. To meet the growing demand for energy, LIB scientists are still working to improve stability in a cyclic search, looking for more stable electrolytes with a voltage window, materials with a positive electrode (cathode) with a higher energy density, and negative cells with a larger capacity.

E1S has always been an effective, nondestructive technique that could analyze/characterize LIBs. The characteristic of the impedance is directly related to the capabilities of the battery and determines the voltage drop observed in the battery when current is applied (Waag, Fleischer, & Sauer, 2013). In Beelen, Raijmakers. Donkers, Notten, and Bergveld (2016), the authors demonstrated the use of IS to estimate battery temperature. It was proved that a simple equivalent circuit can imitate the behavior of the charge-discharge LIB (Liaw, Jungst, Nagasu- bramanian, Case, & Doughty, 2005). Many authors have shown that equivalent circuit models are the best choice for electric vehicle applications, compared to other physical models that require many parameters for model development (Franco, 2013). Deficiencies in this type of simulation exist, since this method is difficult to use in the design process of the cell, but these models are preferred in battery management applications (Fotouhi, Auger, Propp, Longo, & Wild, 2016). EIS method can be performed at different levels, either at the level of the electrodes (Andre et al., 2011) or at the level of the pouch cell. It can also be used for characteristics that go beyond lithium-ion technologies such as lithium-sulfur and lithium-air (Canas et al., 2013). Real-time impedance measurement methods have also been proposed for bag cells using inputted noise or signal; it also uses an algorithm that is used to estimate the impedance parameters from the model (Lohmann, WeBkamp. HauBmann, Melbert. & Musch, 2015). Fast Fourier transform is commonly used for signal detection (Christophersen, Motloch, Morrison. Donnellan, & Morrison, 2008). This is done to assess the state of battery health (Eddahech, Briat, Bertrand, Deletage. & Vinassa, 2012). Impedance studies are typically conducted to analyze the effect of parameters with respect to temperature, state of charge (SoC), and current velocity, as well as to quantify the health status and aging effect under various cycling/storage conditions. There have been several studies related to temperature and SoC studies in the LIB (Samadani et al., 2015). For aging studies, EIS was used as part of the verification procedure to quantify the change in impedance relative to the impedance of a new cell. This can give an idea of which cyclic conditions (SoC, current speed, or temperature) have a greater impact on battery life. Such a study was performed in European project on nickel manganese cobalt oxide cells [Batteries2020.eu... Towards Competitive European Batteries www. batteries2020.eu] and several other works, such as ISO 12405-3:2014 - Electrically propelled road vehicles https:llwww.iso.orglstandardl59224.html. Based on these results, it is possible to select operating conditions that include security protocols, application, and the working environment.

In EIS study by Gopalakrishnan et al. (2019), a commercially available 20 Ah LIB (G1 - commercial cell) and a 28 Ah prototype (G2 - prototype) with the chemical composition of nickel-manganese cobalt oxide/graphite are used to determine the contribution of temperature and SoC to EIS. The SoC of the cell plays an important role in charge transfer processes in cells. The semicircle size in the Nyquist diagram is a criterion for the SoC of the cell. Its increase corresponds to a decrease in charge, which is also seen in Figure 4 in Gopalakrishnan et al. (2019).

Gopalakrishnan et al. (2019) have showed that advertising G1 cells work better in terms of less increase in charge transfer resistance compared to G2 cells, which means that G1 cells can protrude on larger SoC window as compared to G2 cells. The electrode structure, particle size, stacking of the electrodes, and other entities for both the cells are provided to compare the similarities and differences between both the cells. Equivalent circuit modeling is used to analyze and comprehend the variation in impedance spectrum obtained for both the cells. It is observed that the ohmic resistance varies with both temperature and SoC and the variation with temperature is more significant for the prototype cell. The prototype cell showed better charge-transfer characteristics at lower temperatures when compared to the commercial cell. Cells of generation 1 (cell G1 - commercial cell) and generation 2 (cell G2 - prototype) that were selected were different depending on various elements, including stoichiometry of the active material, particle size of the active material, electrode stacking, electrode architecture, separator, and electrolyte. The impedance spectrum of these two cells was studied as a function of SoC and temperature. Two equivalent circuits, one for low temperature and low temperature SoC, the second for all other conditions, were used to extract parameters from two different types of cells. CPEs were used to simulate the double layer capacity, as well as the diffusion process, since the semicircles obtained for both cells were depressed and the diffusion tail was not 45°. It was found that cells G1 have a lower ohmic resistance compared to cells G2 at all temperatures and SoC conditions, which can be associated with electrolyte solvents and, possibly, a separator (electrolyte absorption). The ohmic resistance varies with temperature and SoC, and the change with temperature is more significant for cell G2. A common reason for the reduced productivity of G2 cells may be due to the morphology of the electrodes and the separator used in the cell.

 
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