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We have investigated the effect of applying external pressure during cell preparation and its further electrochemical behavior as a Li-ion battery electrode.

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Li‐ion batteries have been of a great interest for over three decades. A geometric electrode surface area is generally used for Li‐ion electrochemical parameters calculations. Since the real electrode is a complex system composed of the thick porous structure, the contact surface area between the active mass and electrolyte is far larger than geometrical. This approximation leads to a large deviation of obtained results, especially within different laboratories and for volume and surface changing materials, e. g., silicon. The article presents a new method of in situ analysis of active surface area variations applicable for Li‐ion electrodes. The method relies on the electrochemical impedance spectroscopy measurement (EIS) performed at an arbitrarily chosen state of charge during superimposed DC current flow. The correlation between a local ion concentration with a charge transfer resistance allows to evaluate the differences of the active surface area. The presented method is not affected by the SEI layer presence, the material composition, nor the lithiation mechanism. Due to limited EIS frequency range the presented method can be performed with a relatively short time. Our new in situ surface area determination can greatly improve the accuracy of the electrochemical parameters evaluation and enable the proper result analysis. We believe that our method can become a standard procedure implemented in every research focusing on the electrochemical parameter determination of the volume changing active materials.

Among the many studied Li-ion active materials, silicon presents the highest specific capacity, however it suffers from a great volume change during lithiation. In this work, we present two methods for the chemical modification of silicon nanoparticles. Both methods change the materials’ electrochemical characteristics. The combined XPS and SEM results show that the properties of the generated silicon oxide layer depend on the modification procedure employed. Electrochemical characterization reveals that the formed oxide layers show different susceptibility to electro-reduction during the first lithiation. The single step oxidation procedure resulted in a thin and very stable oxide that acts as an artificial SEI layer during electrode operation. The removal of the native oxide prior to further reactions resulted in a very thick oxide layer formation. The created oxide layers (both thin and thick) greatly suppress the effect of silicon volume changes, which significantly reduces electrode degradation during cycling. Both modification techniques are relatively straightforward and scalable to an industrial level. The proposed modified materials reveal great applicability prospects in next generation Li-ion batteries due to their high specific capacity and remarkable cycling stability.