| Graphite is currently the most common commercial anode material for Li-ion batteries which has a theoretical capacity value of 372 mAh/g. Since this value has already been achieved and does not fulfill the requirements of new technologies, replacement of carbon with new anode materials has become a necessity. Recently, silicon (Si) has been proposed as a promising anode material because of its high theoretical capacity (∼3580-4200 mAh/g), which is the highest known value among all materials in nature so far. However, Si anode materials suffer from several problems which have prevented its commercial use. The most significant problem with bulk Si is its more than ∼400% volume change during the insertion/extraction of lithium ions. This high volumetric expansion/contraction of in Si structure causes considerably high stress followed by cracking, pulverization, and the loss of electrical contact; and finally results in capacity fading and failing. In order to achieve higher cycling performance without pulverization and delamination, the mechanical failure due the volume change must be tolerated. Studies reported in the literature suggested several approaches to overcome the problems associated with Si/Li intercalation. Using active and inactive additives, coatings on Si, Si-C composites, and composite nanostructures and films have been considered for this purpose. However, these methods were successful to a certain extent addressing only some of the problems, yet not being able to solve the major challenges with Si.;In this work, we developed a new density modulated multilayer Si thin film anode approach, which can provide a robust high capacity electrode for Li-ion batteries. Our results showed that these films can provide a high coulombic efficiency up to 99% and reversible specific capacity as high as ∼1700 mAh g-1 after 50 cycles. Low-density layers are believed to be performing as compliant layers during volume change making the films more durable compared to conventional Si film anodes. Several materials such as Cr and Ni were also tested as adhesion layers to overcome the delamination problem. The results of this work can lead to Si thin film anode materials with superior capacity and mechanical stability compared to conventional Si anodes. |
