Coin Cells

Fig. 23. Cutaway view of (a) 2016-size Eveieady lithium manganese dioxide coin cell, and (b) jelly toll cylindrical lithium manganese dioxide cell (28).

For convenience and simplicity, the electrochemical study of electrode materials is normally made in lithium/(eleetrode material) eells. For earbonaeeous materials, a hthium/carbon eell is made to study electroehemical properties, sueh as eapaeity, voltage, eyeling life, etc.. Lithium/carbon coin cells use metallie lithium foil as the anode and a partieular carbonaceous material as the... 

Lithium/carbon cells are typically made as coin cells. The lithium/carbon coin cell consists of several parts, including electrodes, separator, electrolyte and cell hardware. To construct a coin cell, we first must prepare each part separately. Successful cells will lead to meaningful results. The lithium/carbon coin cells used metallic lithium foil as the anode and a carbonaceous material as the cathode. The metallic lithium foil, with a thickness of 125 pm, was provided by Moli Energy (1990) Ltd.. Idie lithium foil is stored in a glove-box under an argon atmosphere to avoid oxidation. 

Electrochemical cells are assembled in the glove-box. The cell is a 2320-type coin cell (23 mm OD and 2.0 mm thickness) as schematically shown in Fig. 5. The cell includes the electrolyte, the cell cap and can which are stainless steel, a polypropylene gasket used to seal the cell, the two electrodes, the separator between the electrodes, as well as a stainless spacer and a mild steel disc spring which are used to increase the pressure on the electrodes. Once the cell is assembled in the right order, the cell is sealed by a pressure crimper inside the glove-box. 

Freshly assembled lithium/carbon coin cells typically have voltages between 2.8 and 3.4 volts. The cells are in their fully charged state which means that no lithium is inserted in the carbon anode. Then the coin cells are tested with computer-controlled constant-current cyclers having currents stable to 1%. The cells are placed in thermostats at a particular set temperature v/hich is stable to 0.1°C during the test. Most of our cells were tested at 30°C. 

There is a trend towards manufacture of Zn-air cells in a larger coin-cell format. 

The alternative alloy anodes which exhibit good cycle life in coin cells (Table 1) are not applied to cylindrical cells. This is because they are brittle and these alloy anodes turn into fine particles after cycling when the anode is spirally wound in the... 

Fignre 27.3 shows a typical spectroelectrochemical cell for in sitn XRD on battery electrode materials. The interior of the cell has a construction similar to a coin cell. It consists of a thin Al203-coated LiCo02 cathode on an aluminum foil current collector, a lithium foil anode, a microporous polypropylene separator, and a nonaqueous electrolyte (IMLiPFg in a 1 1 ethylene carbonate/dimethylcarbonate solvent). The cell had Mylar windows, an aluminum housing, and was hermetically sealed in a glove box. 

Coin Cell Mockups of Rechargeable Metal-Air Batteries... 

Figure 5. Galvanostatic charge/discharge curves of the coin cell mockups of Zn-Air battery...

For purposes of verifying of the concept of a self-discharge due to the LEM oxidation by air, we have designed a coin cell with a zinc electrode and a thin PANI/TEG cathode. The typical curves of voltage change for such electrochemical device are given by Figure 6. 

In the next paper by Y. Illin et al., capabilities of Sn anodes are considered as a possible alternative to carbon. Thin films of Sn were deposited onto current collector in vacuum, and tested in the coin cells. Authors were able to obtain reversible alloying reaction, which stabilized at 100 mAh/g between cycle number 100 and 400. The stability of Sn and its characteristics upon cycling was seen to be a function of the current collector material. The best results were achieved with non-copper-based substrates. 

Figure 1. Typical galvanostatic charge (1) - discharge (2) curves of the lithium-ion battery grade graphite, SL-20 (Superior Graphite Co., USA), as tested at C/20 rate in 2016 coin cells having Li metalfoil as counter electrode and electrolyte EC.DMC + lMLiPFf,.

Table 1. Results of initial galvanostatic cycling of experimental 2016 coin cells with different types of graphite from SGC at C/20 rate (AU = 0.01 - 1.0V). Electrolyte - LP-30 from Merck (EC DMC + IMLiPFS). Counter electrode - Li foil.

Results for an average sample in a series of 3-5 coin cells, during the first 4-5 cycles. According to the Product Information Bulletins of SGC Purified Battery Grade Graphite. 

All samples were galvanostatically tested in coin cell 2016 semielements and special Teflon T-type testing cells in the potential window 0.03 - 0.80 V versus lithium foil in different modes from C/2 to C/40. We used standard electrolyte LP 71 (Merck). 

Initially, cycling in the coin cells, and later, in full prismatic cells with rated capacity of 7 Ah were used in our investigations. Also, advanced impedance spectroscopy methods were used to evaluate the electrochemical properties of coated materials. 

Both carbon materials were tested for their initial electrochemical performance in the 2-electrode electrochemical cells with Li metal as a counter electrode. Our findings have shown that with both types of carbon materials, achieving near theoretical reversible capacity upon Li+ deintercalation was possible. Thus, in a typical half cell environment (a CR2016 type coin cell with graphite and Li metal electrodes, a 1M LiPF6,... 

The comparative 2016 coin cell data of the uncoated vs. Si-coated spheroidized natural graphite precursor vs Li metal counter electrode (Figure 5) reveals a remarkable effect of metal addition onto the reversible capacity of anode. Thus, the starting material s reversible capacity increased from approximately 350 mAh/g to over 510 mAh/g (data taken at 0.8V vs Li/Li+), which is 1.37 times higher than the theoretical value of the reversible capacity for graphite. 

Carbon coated Si-based anode materials were successfully synthesized by chemical vapor deposition methods. Coated materials performed well during the coin cell testing. Future work on this section... 

Further on, the Co-Ni complexes were used for modification of Hohsen Carbon type (10-10) and Hohsen Graphite type (10-28) anode materials for Li-ion batteries applying similar procedure. These anode materials were tested in 2016 size lithium coin cells with a configuration Li/electrolyte (LP-30)/(modified anode material). The coin cells were assembled by standard technology in dry atmosphere of a glove box and then... 

C for 10-14 h in an alumina tray inside a Lindberg tube furnace under controlled gas flow. On some occasions, and as a control experiment, pure argon gas was employed during the annealing step. Resultant powders were used in electrochemical (coin cell cycling) studies. 

In the fifth paper of this chapter on cathodes, an investigation of thin-film oxide-hydroxide electrodes containing Cr, Ni, and Co compounds was authored by N. Vlasenko et al. The thin-films were produced by electrochemical deposition from transition metal aqueous fluorine-containing electrolytes onto steel substrates. These thin-films were tested in Li coin cells. Electrochemical activity appears to scale with the amount of fluoride used in the deposition the larger concentration of fluoride in the bath, the greater the capacity. One Ni oxide-hydroxide film electrode showed greater than 175 mAh/g reversible capacity on the 50th cycle with excellent coulombic efficiency. 

Figure 1. Discharge curves for 2325 coin cells with lithium metal anodes and electrolytic (crystalline) vs amorphous manganese oxide-based cathodes.

Table 1. Performance parameters of2325 coin cells, as obtainedfrom galvanostatic cycling regime (0.5 mA).

There are many ways to characterize the structure and properties of carbonaceous materials. Among these methods, powder X-ray diffraction, small angle X-ray scattering, the BET surface area measurement, and the CHN test are most useful and are described briefly here. To study lithium insertion in carbonaceous materials, the electrochemical lithium/carbon coin cell is the most convenient test vehicle. 

Pelham, H. R. and Rothman, J. E. The debate about transport in the Golgi-two sides of the same coin Cell 102 713-719, 2000. 

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