Diffusion of Li-ions

Figure 8.14 Huggins analysis of a Warburg element in a Nyquist plot such as that shown in Figure 8.12(a), for the diffusion of Li" ions through solid-state WO3. The traces for Z and Z" against will not be parallel for features other than that of the Warburg. From Ho, C., Raistrick, I. D. and Huggins, R. A., Application of AC techniques to the study of lithium diffusion in tungsten trioxide thin films , J. Electrochem. Soc., 127, 343-350 (1980). Reproduced by permission of The Electrochemical Society, Inc.

CastigUone, F. Ragg, E. Mele, A. Appetecchi, G. B. Montemino, M. Passerini, S., Molecular Environment and Enhanced Diffusivity of li+ Ions in Lithium-Salt-Doped Ionic Liquid Electrolytes. J. Phys. Chem. Lett. 2011,2, 153-157. 

Note that the time required to fill the particle half full with hydrogen depends on the square of the particle radius (R ). Thus, a particle that is twice as large would require four times longer to fill. This dependence provides a powerful motivation to use nanoscale particles to improve the kinetics of hydrogen stor-age/release in metal hydrides and also motivates the use of nanoscale particles in applications such as Li ion batteries, where diffusion of Li ions into and out of the electrode particles often controls the rate capacity of the battery. 

The observed T diffusivity in this material was the largest then known for Li-based oxide ceramics. This corresponded with the fact that the diffusivity of Li ions in crystals was the largest known for these ceramics. 

Nanoparticulate electrode materials are considered by many as a viable solution to the limitations in the rate capability of Li-ion batteries [17-19]. The charge and discharge current rate limitations are mainly caused by slow solid-state diffusion of Li ions in the electrode materials [19,20]. Amongst the potential advantages of nanoparhcles are ... 

A dry cell is not truly dry, because the electrolyte is an aqueous paste. Solid-state batteries have been developed, however. One of these is a lithium-iodine battery, a voltaic cell in which the anode is lithium metal and the cathode is an I2 complex. These solid-state electrodes are separated by a thin crystalline layer of lithium iodide (Figure 20.11). Current is carried through the crystal by diffusion of Li" ions. Although the cell has high resistance and therefore low current, the battery is very reliable and is used to power heart pacemakers. The battery is implanted within the patient s chest and lasts about ten years before it has to be replaced. 

It is known that it is difficult to attain the full capacity because the electronic conductivity of LiFeP04 is very low, which leads to initial capacity loss and poor rate capability, and diffusion of Li ion across the LiFeP04/FeP04 boundary is slow due to its intrinsic character [16]. Therefore, to improve electrochemical performance of LiFeP04, we should control particle sizes and morphology [43-44, 53, 71, 76, 93, 104-115], as mentioned in section 3.1. Recently, it is found that ionic substitution is another feasible way to enhance the intrinsic electronic conductivity [116-131]. 

It must have an optimized crystal structure suitable for the diffusion of Li+ ions into the Mn02 crystal lattice. 

Considering the effect of stress-driven diffusion, the diffusion of Li-ions inside an electrode particle can be described as... 

Nanomaterials have more crystal boundaries to provide channels for rapid diffusion of Li+ ions. 

In the case of nanostructured porous LiFeP04, on the one hand, the diffusion of Li+ ions is increased. On the other hand, overcoming the effects of low volumetric energy density and the effect of the possible collapse of the pores on the electrochemical performance of LiFeP04 should be considered. 

Since highly dispersed inert phases are produced, the diffusion of Li+ ions through the interfaces is increased. The reversible capacity increases to 900-950 mAh/g, which is higher than that of the terminal component of Li44Sn due to the existence of Si. 

Finally, the model has been confirmed by spectroscopic analysis. Raman results reported by Best et al. have demonstrated the specific interaction between nanometric Ti02 powders and the salt. In addition, NMR data have shown that the diffusion of Li ions, and thus the related T+ value, in the nanocomposite electrolytes, is considerably higher than that of the parent ceramic-free electrolytes. 

---