Lithium electrode porosity

Electrode porosity is also an important parameter. Consistent with findings of Kuboki et al. [20], Xiao et al. [22] found that the capacity of lithium-air batteries increases with increasing mesopore volume of the carbon used in the air electrode. They also found that there is an optimized carbon loading (or thickness) for the air electrode. 

In addition to the criticisms from Anderman, a further challenge to the application of SPEs comes from their interfacial contact with the electrode materials, which presents a far more severe problem to the ion transport than the bulk ion conduction does. In liquid electrolytes, the electrodes are well wetted and soaked, so that the electrode/electrolyte interface is well extended into the porosity structure of the electrode hence, the ion path is little affected by the tortuosity of the electrode materials. However, the solid nature of the polymer would make it impossible to fill these voids with SPEs that would have been accessible to the liquid electrolytes, even if the polymer film is cast on the electrode surface from a solution. Hence, the actual area of the interface could be close to the geometric area of the electrode, that is, only a fraction of the actual surface area. The high interfacial impedance frequently encountered in the electrochemical characterization of SPEs should originate at least partially from this reduced surface contact between electrode and electrolyte. Since the porous structure is present in both electrodes in a lithium ion cell, the effect of interfacial impedances associated with SPEs would become more pronounced as compared with the case of lithium cells in which only the cathode material is porous. 

Preferably, the lithium ion battery separators range in average fiber diameter from 1-3 p, and in basis weight from 10-20 g m-2 The average fiber diameter and basis weight are substantially the same before and after the pressing. The lithium ion battery separator desirably has a porosity of 40 to 50%, and a thickness of 20-45 p. A lithium ion battery separator with this porosity value provides a low internal resistance and does not pass electrode substances to prevent short circuits. The thickness in the above range is suitable for the separator to be applied to small sized lithium ion batteries (21). 

The necessary porosity for thicker layers was introduced by appropriate current densities [321-323], by co-deposition of composites with carbon black [28, 324] (cf. Fig. 27), by electrodeposition into carbon felt [28], and by fabrication of pellets from chemically synthesized PPy powders with added carbon black [325]. Practical capacities of 90-100 Ah/kg could be achieved in this way even for thicker layers. Self-discharge of PPy was low, as mentioned. However, in lithium cells with solid polymer electrolytes (PEO), high values were reported also [326]. This was attributed to reduction products at the negative electrode to yield a shuttle transport to the positive electrode. The kinetics of the doping/undoping process based on Eq. (59) is normally fast, but complications due to the combined insertion/release of both ions [327-330] or the presence of a large and a small anion [331] may arise. Techniques such as QMB/CV(Quartz Micro Balance/Cyclic Voltammetry) [331] or resistometry [332] have been employed to elucidate the various mechanisms. 

Lee, H.,Yoo, J.K., Park, J.H., Kim, J.H., Kang, K., Jung,Y.S., 2012. A Stretchable polymer-carbon nanotube composite electrode for flexible lithium-ion batteries porosity engineering by controlled phase separation. Adv. Energy Mater. 2,976-982. 

The bulk of EAP-based supercapacitor work to date has focused on Type I devices. Polypyrrole (PPy, Figure 9.4C) has been studied [147,151-153] for this application, with specific capacitance values ranging from 40 to 200 F/g. Garcia-Belmonte and Bisquert [151] electrochemically deposited PPy devices that exhibit specific capacitances of 100-200 F/cm with no apparent dependence on film thickness or porosity extensive modeling of impedance characteristics was used. Hashmi et aL [153] prepared PPy-based devices using proton and lithium-ion conducting polymer electrolytes. As is often observed, electrochemical performance suffered somewhat in polymeric electrolytes single electrode specific capacitances of 40-84 F/g were observed with stability of 1000 cycles over a 1 V window. 

Thionyl chloride, sulphuryl chloride or sulphur dioxide where the solvent is also the electroactive species at the positive electrode, made from a high surface-area, high-porosity carbon. In thionyl and sulphuryl chloride cells the electrolyte is usually lithium tetrachloroaluminate while sulphur dioxide is... 

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