Li diffusion

In specific, it was found that up to 3.5 mole lithium per mole molybdenum can be intercalated in films with high oxygen content and 1.7 in the others. The Li diffusion coefficient was found equal to 10 cm s at the beginning of the intercalation. It was noted that intercalation of the first Li is never reversible. 

The Li ions were introduced in two different ways either before or after Zr intercalation. The montmorillonite (Weston L-Eccagun) was first exchanged with NaCl (IN) and washed. Two montmorillonites with reduced charge were prepared following the Brindley and Ertem method (13). Part of the Na+ montmorillonite was first saturated with LiCl (IN) and washed. The Li+ clay thus obtained and Na+ clay suspension were stirred for 24 hours at 25°C and dried on glass plate. The films were then heated at 220°C for 24 h in order to allow Li diffusion in the clay structure. Two different Li concentrations (F=0.4 and F=0.6) were used. The Na Li+ modified montmorillonite were dispersed in water acetone solution (1/1). The ZrOCla, 8H2O solution was added to the Na+Li+ montmorillonite (0.02g.l l Zr/Clay=5.CEC). The suspension was stirred with NaOH solution (0.1 N) up to a OH/Zr ratio of 0.5. The final pH of the suspension was 1.85. After two hours of reaction at 40°C the Zr pillared clay was washed up to constant conductivity of the solution, freeze-dried and calcined at different temperatures up to 700°C (Eni-02 and EIII-03). 

The Li diffusion in the clay structure slightly enhances the acidity of the Zr pillared montomorillonite as shown by the variation of the amount of desorbed NH3 We also observed a parallel decrease of the Lewis and increase of the Brdnsted sites. 

At the anode, metallic lithium dissolves as lithium ion (Li+) and, at the cathode, Li+ diffuses into the crystal lattice of manganese dioxide. 

There are reports that the surface chemistry of Li alloys is indeed largely modified, compared with Li metal electrodes [303], It appears that they are less reactive with solution species, as is expected. The morphology of Li deposition on Li alloys may also be largely modified and smooth, compared with Li deposition on Li substrates [302,304], A critical point in the use of Li alloys as battery anodes is the lithium diffusion rates into the alloys. Typical values of Li diffusion coefficient into alloys are 3-LiAl —> 7 16 9 cm2/s [305], Li44Sn —> 2 10 9 cm2/s [306], LiCd and LiZn —> 1010 cm2/s [307], It should be emphasized that it is very difficult to obtain reliable values of Li diffusion coefficient into Li alloys, and thus the above values provide only a rough approximation for diffusion rates of Li into alloys. However, it is clear that Li diffusion into Li alloys is a slow process, and thus is the rate-limiting process of these electrodes. Li deposition of rates above that of Li diffusion leads to the formation of a bulk metallic lithium layer on the alloy s surface which may be accompanied by mas-... 

New methods for CT analysis and an explanation for the existing discrepancy in Li diffusivity values obtained by the diffusion control CT analysis and other methods. 

To study the mobility of Li" " on the gel matrix, we measured the Li diffusion coefficient before and after gelation of the 2-Li (with 5 wt% PAMPSLi) using pfg-NMR. The Li diffusion coefficient in the gel was almost unchanged from the value before gelation, despite the decrease in the ionic conductivity with gelation. Because, as this result suggests, the mobility of Li is not suppressed by gelation, this gel system is favorable for Li" " conductive materials. 

The electrochemical reduction of Ti02 is known to be accompanied by the intercalation of small cations. This finding has been explored in sensitizing anatase films for battery applications [149]. Cation coordination to titanium alkoxide sol-gel precursors is also well known [150]. Lyon and Hupp used quartz crystal microbalance techniques to determine the mass of intercalating cations as the TiOa film is reduced [151]. Hagfeldt and co-workers have studied Li+ and Na intercalation into anatase Ti02 both theoretically and experimentally [152, 153). They found that the diffusion constants for Li and Na+ are temperature dependent with an activation barrier of 0.4 eV for insertion and 0.5 eV for extraction. The Li+ diffusion coefficient at 25 °C into the nanoporous structure was approximately 2 X 10 cm s for insertion and 4 x 10 cm s for extraction. 

Metallic Li deposited on Si and Ge surfaces is heated in a closed tube in a He atmosphere at 450-1000°CL The Li-diffused layer is n-type. The doping layer consists of Li2Si -I- Si, especially above the eutectic temperature of 650°C. The dimorphic silicide, Li4Si, may also be formed, depending on the composition of the Li-Si compound. ... 

THF was damaged by che electron beam used in AES and the x-rays in XFS and this behavior was carefully examined. In addition, Li diffusion into che Ag substrate will be discussed. 

Ignatiev that Li diffuses into graphite even at liquid nitrogen temperature to leave only a submonolayer of Li on the surface. Diffusion of other alkali metals (Na, K, and Rb) into silver has also been observed by Lambert and co-workers but is significant only at high temperatures (> 870 K). Li diffuses more readily because of its small size. The atomic radii for Li, Na, K, Rb and Cs are 1.55, 1.90, 2.35, 2.48 and 2.67 A respectively. 

A major concern was whether at least one full monolayer of metallic Li would remain on the Ag surface after a multilayer Li/Ag sample covered with THF was warmed to room temperature in about 45 minutes. Figure 5.6 shows a typical AES spectrum of a 95%Li/Ag surface exposed to 50 L THF at 113 K and then warmed to room temperature. It was estimated based on AES that the amount of Li remaining on the surface was about 80%, corresponding to about 14 monolayers of Li. The reduction from 95% to 80% may be in part due to the presence of THF on the sample. This proved that the results of experiments conducted below room temperature are due to reaction with Li and not with Ag or of the competition with Li diffusion. As will be described later, some of the Li reacted with THF when the THF/Li/Ag was warmed to room temperature. This slowed the diffusion of Li. 

The reaction of THF (tetrahydrofuran) with Li was studied. THF adsorbed on deposited Li films with partial dissociation, yielding less than a monolayer mixture of THF and dissociated products on the surface. It was observed that Li diffused into Ag above room temperature. The electron beam in AES and x-rays in XPS caused severe damage to THF. 

Lithium transport through transition metal oxides and carbonaceous materials is of paramount importance in rechargeable lithium batteries. The chapter by Drs. H. -C. Shin and Su-11 Pyun from KAIST, Korea, examines critically the diffusion control models, used routinely for current transients (CT) analysis, and demonstrates that, quite frequently, the cell current is controlled by the total cell impedance and not by lithium diffusion alone. This interesting chapter, rich in new experimental data, also provides a new method for CT analysis and an explanation for the existing discrepancy in Li diffusivity values obtained by the diffusion control CT analysis and other methods. 

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