Reactivity, Protection, and Side Reactions

Side reactions can introduce error into the measurement of physical properties in three ways [73]. Current is consumed by the side reaction, introducing error into calculations of the amount of current that went into the main reaction. Bulk concentrations of salt or solvent may change if the side reaction is substantial, and soluble products of reaction may affect the activity of the electrolyte. Finally, the side reaction causes the potential of the electrode to be a mixed (corrosion) potential. It is commonly assumed that the lithium electrode is covered by the SEI layer. However, there is strong evidence that, in many situations, the protection is not complete and side reactions involving the solvent or anion continuously occur. Such reactions can increase the concentration of lithium ions adjacent to a lithium electrode, introducing error into measurements of the variation in potential with apparent electrolyte concentration, particularly at low electrolyte concentrations. Such concentration-ceU measurements are used to obtain activity coefficients and transference numbers via the galvanostatic polarization method. Simulations of the type described in this section can be used to analyze how much error is introduced by the side reaction [73]. It may be preferable to use a less reactive reference electrode, such as Li4Ti50,2 [74], to reduce this error. 

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