SEI composition and morphology

Figure 17. The basal plane and prismatic surfaces of graphite have different functions with respect to lithium intercalation and de-intercalation (= charge, discharge, self-discharge, etc.). As a consequence, only the electrolyte decomposition product layers at the prismatic surfaces have SEIfunction. Any processes related with electrolyte decomposition product layers at the basal plane surfaces (= non-SEI layers) therefore can not be directly related to electrochemical data such as charge, discharge, self-discharge, etc. The situation is even more complex as the SEI composition and morphology at the basal and prismatic surface...

Peled E., Golodnitsky D., Ulus A., Yufit V. Effect of carbon substrate on SEI composition and morphology, Electrochim. Acta 2004, 50, 391-395. 

The chemical composition of the SEI formed on carbonaceous anodes is, in general, similar to that formed on metallic lithium or inert electrodes. However some differences are expected as a result of the variety of chemical compositions and morphologies of carbon surfaces, each of which can affect the i() value for the various reduction reactions differently. Another factor, when dealing with graphite, is solvent co-intercalation. Assuming Li2C03 to be a major SEI building material, the thickness of the SEI was estimated to be about 45 A [711. 

Andersson AM, Edstrom K (2001) Oiemicai composition and morphology of the elevated temperature SEI on graphite. J Electrochem Soc 148(10) A1100-Al 109... 

This chapter addresses several issues dealing with the mechanism of SEI formation on inert substrates, lithium, carbonaceous materials and tin-based alloys. Attention is currently focused on the correlation between the composition and morphology of the solid-electrolyte interphase forming on the different planes of highly ordered pyrolytic graphite (HOPG) and different types of disordered carbon electrodes in lithium-ion cells. 

It is now generally accepted that the surface chemistry and morphology of the edge planes of graphite play a major role in the chemical and electrochemical reactivity of this material in contact with electrolyte. In order to determine whether there is a correlation between the composition and morphology of the SEI formed on the HOPG and on the real anode in lithium-ion batteries, we... 

Chemical Composition and Morphology of the SEI 16.2.2.1 Ether-Based Liquid Electrolytes... 

The SEI is formed by parallel and competing reduction reactions and its composition thus depends on i0, t], and the concentrations of each of the electroactive materials. For carbon anodes, (0 also depends on the surface properties of the electrode (ash content, surface chemistry, and surface morphology). Thus, SEI composition on the basal plane is different from that on the cross—section planes. 

It should be noted here, that not only the (chemical and morphological) composition of the protective layers at the basal plane surfaces and prismatic surfaces is different, but that these layers also have completely different functions. At the prismatic surfaces, lithium ion transport into/ffom the graphite structure takes place by intercalation/de-intercalation. Here the formed protective layers of electrolyte decomposition products have to act as SEI, i.e., as transport medium for lithium cations. Those protective layers, which have been formed on/at the basal plane surfaces, where no lithium ion transport into/from the graphite structure takes place, have no SEI function. However, these non-SEI layers still protect these anode sites from further reduction reactions with the electrolyte. 

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