Li electrodes

Graphite, KS44, Lonza EC. DEC/LiPF6 FTIR Few (Li02C0CH2)2 (from EC), Li2CO, in contrast to Li electrodes f200 ... 

This distribution causes a problem the best-described conducting polymers interchange anions with the electrolyte, and the Li electrode liberates Li+during discharge. The salt accumulates in the electrolyte [Fig. 32(a)], requiring a great volume and mass in order to avoid the precipitation of the salt. This fact reduces the specific energy of the battery to impractical values. 

Self-Test 4A Write the diagram for a cell with a hydrogen electrode on the left and an irnn(III)/irnn(lI) electrode on the right. The two electrode compartments are connected by a salt bridge and platinum is used as the conductor at each electrode. 

As the reduction potential for (CH),/(CH ) is approx. 0.5 to 1 V positive to the Li" /Li electrode, reducing neutral PA with a positive EMF produces an energy gain (cell type 2) 2 W-246.25o,25d jjjg complete cell reaction is then ... 

Electrochemical studies were carried out in the above cation-deficient thiospi-nel. The cyclic voltammogram of Cu5.5SiFe4Sni2S32 in 1 M LiBF4 electrolyte between 1 and 4.6 V versus the Li/Li electrode is given in Fig 15.6. However, no clear peaks could be observed in the CV plot. 

Fig. 5.35 SNIFTIRS spectrum from a polished Pt electrode in 0.5 m LiC104 in propylene carbonate. Reference potential 2.00 V versus Li/Li+ electrode working potential 3.20 V versus Li/Li+ electrode. According to P. Novak et al.

Fig. 12.3 Fabrication of the nanocomposite paper units for battery, (a) Schematic of the battery assembled by using nanocomposite film units. The nanocomposite unit comprises LiPF6 electrolyte and multiwalled carbon nanotube (MWNT) embedded inside cellulose paper. A thin extra layer of cellulose covers the top of the MWNT array. Ti/Au thin film deposited on the exposed MWNT acts as a current collector. In the battery, a thin Li electrode film is added onto the nanocomposite, (b) Cross-sectional SEM image of the nanocomposite paper showing MWNT protruding from the cel-lulose-RTIL ([bmlm] [Cl]) thin films (scale bar, 2pm). The schematic displays the partial exposure of MWNT. A supercapacitor is prepared by putting two sheets of nanocomposite paper together at the cellulose exposed side and using the MWNTs on the external surfaces as electrodes, (c) Photographs of the nanocomposite units demonstrating mechanical flexibility. Flat sheet (top), partially rolled (middle), and completely rolled up inside a capillary (bottom) are shown (See Color Plates)...

Fig. 12.3 Fabrication of the nanocomposite paper units for battery, (a) Schematic of the battery assembled by using nanocomposite film units. The nanocomposite unit comprises LiPF6 electrolyte and multiwalled carbon nanotube (MWNT) embedded inside cellulose paper. A thin extra layer of cellulose covers the top of the MWNT array. Ti/Au thin film deposited on the exposed MWNT acts as a current collector. In the battery, a thin Li electrode film is added onto the nanocomposite.

A second major event in the saga of polymer conductors was the discovery that the doping processes of polyacetylene could be promoted and driven electrochemically in a reversible fashion by polarising the polymer film electrode in a suitable electrochemical cell (MacDiarmid and Maxfield, 1987). Typically, a three-electrode cell, containing the (CH) film as the working electrode, a suitable electrolyte (e.g. a non-aqueous solution of lithium perchlorate in propylene carbonate, here abbreviated to LiC104-PC) and suitable counter (e.g. lithium metal) and reference (e.g. again Li) electrodes, can be used. 

Electroneutrality demands that a concentration gradient exists for both lithium and triflate near the Li electrode and that the diffusion is coupled in a similar fashion to the coupled diffusion of ions and electrons in intercalation electrodes (Chapter 8). As in that case it is the coupled diffusion of both species which is observed, i.e. the salt diffusion coefficient. This may be evaluated by fitting the low frequency region of the curve to ... 

This reactiyity does not appear with bars or foils of metallic Li, but only with a cycled Li electrode. If rechargeable Li SBs are to be practical, a means to control the morphology of Li must be found (45b). 

In the lithium-ion secondary battery, which was put on the market in 1990, the difficulty of the Li+/Li electrode was avoided by use of a carbon negative electrode Cy), which works as a host for Li+ ions by intercalation. The active material for the positive electrode is typically LiCo02, which is layer-structured and also works as a host for Li+ ions. The electrolyte solutions are nearly the same as those used in the primary lithium batteries. A schematic diagram of a lithium-ion battery is shown in Fig. 12.2. The cell reaction is as follows ... 

Electrochemical deposition of lithium usually forms a fresh Li surface which is exposed to the solution phase. The newly formed surface reacts immediately with the solution species and thus becomes covered by surface films composed of reduction products of solution species. In any event, the surface films that cover these electrodes have a multilayer structure [49], resulting from a delicate balance among several types of possible reduction processes of solution species, dissolution-deposition cycles of surface species, and secondary reactions between surface species and solution components, as explained above. Consequently, the microscopic surface film structure may be mosaiclike, containing different regions of surface species. The structure and composition of these surface films determine the morphology of Li dissolution-deposition processes and, thus, the performance of Li electrodes as battery anodes. Due to the mosaic structure of the surface... 

Hence, a key point in the study of the behavior of Li electrodes is the correlation among the surface chemistry (determined by the solution composition), morphology, and reversibility during repeated deposition-dissolution cycles. Some highlights in these studies are outlined below ... 

Intensive work was carried out in the seventies by Dey et al. [69-71], Koch et al. [72-74], Jansta et al. [75,76], and Thevenin et al. [77-80] on the chemical analysis of the surface films formed on Li electrodes in solutions. These efforts, however, were based on XPS, AES, and some indirect methods. 

The effect of the stack pressure on the morphology of Li electrodes was studied by Wilkinson et al. [106], This issue is highly important, as applying stack pressure on Li electrodes considerably suppresses dendrite formation during Li deposition. 

The application of novel in situ spectroscopic techniques for the study of Li electrodes in solutions should also be acknowledged. These include FTIR spectroscopy [108], atomic force microscopy (AFM) [109], electrochemical quartz crystal microbalance (EQCM) [110], Raman spectroscopy [111], and XRD [83],... 

A great deal of effort was dedicated to the study of Li electrodes in polymeric electrolyte systems [112-115], These can serve as alternatives for the liquid electrolyte solutions in which dendrite formation is such a severe problem. 

Table 2 Some Review Articles on Li Electrodes and Li Batteries...

---