Morphology lithium battery electrodes

Both batteries and fuei cells utilize controlled chemical reactions in which the desired process occurs electrochemically and all other reactions including corrosion are hopefully absent or severely kinetically suppressed. This desired selectivity demands careful selection of the chemical components including their morphology and structure. Nanosize is not necessarily good, and in present commercial lithium batteries, particle sizes are intentionally large. All batteries and fuel cells contain an electropositive electrode (the anode or fuel) and an electronegative electrode (the cathode or oxidant) between which resides the electrolyte. To ensure that the anode and cathode do not contact each other and short out the cell, a separator is placed between the two electrodes. Most of these critical components are discussed in this thematic issue. 

For the synthesis of polyaniline designed for battery electrodes, Fe(C104)3 and Cu(BF4)2 are preferable as oxidizing agents, because the products contain CIO 4 or BFi anions, which are commonly used in lithium secondary batteries. Polyaniline synthesized by Cu(Bp4)2 has a fibrous morphology [57],... 

The aim of this study was to lead simultaneously a double approach, experimental and theoretical, to build a phenomenological model able to describe the data collected on positive electrodes (mainly LiCo02 and LiNi02). What is at stake is considerable isolating the relevant parameters that permit to describe and govern the interfacial mechanisms and more specifically the adsorption and insertion mechanisms. This will permit later on to stipulate the conditions of the optimization of the performances of the Lithium batteries (structure, morphology, interface, insertion rate, number of cycles, time, etc.). 

As can be seen, even in Fig. 6.26 deviations from the conformity to a second Pick s law reveal the influence of the surface reaction. This point will be developed in Section 6.7, while the interpretation of the values is described in the next section. Not only dissolution of gaseous components is of importance. Of special significance is the introduction of Li in LixM02 (M= Ni,Co,V, see Section 7.4.3) as a so-called intercalation process ( guest-host-reaction ) which can occur there over a wide range of compositions with invariant morphology. The latter point is relevant if this reaction is made use of in electrochemical applications (electrode function in lithium-batteries, see Section 7.4). 

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... 

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-... 

---