INT | Research Unit Janek

High-Capacity Anodes

In order to improve the energy density of state-of-the-art lithium-ion batteries, either new insertion/intercalation materials or different storage mechanisms are required, among others. A promising anode material is silicon. It conducts an alloying reaction with lithium, leading to theoretical specific capacities of 4008 mAh/g when fully lithiated to a composition of Li21Si5 or 3580 mAh/g for Li15Si4. These values are an order of magnitude higher than that of commonly used graphite, where lithium is intercalated between the graphene planes. Because silicon operates in a comparable potential window, it has been widely discussed as a replacement for graphite in lithium-ion batteries. However, despite the progress made in recent years, there are still many open questions related to the stability and safety that need to be addressed before commercialization of electrodes with both high content of silicon and high mass loading can be contemplated. Overall, our research aims at devising strategies to achieve the goal of improving the cycling performance of high-capacity silicon anodes.

Advanced Analytics

Because knowledge of mechanical degradation resulting from volume changes during battery operation and other detrimental side reactions such as gassing due to continuous electrolyte decomposition is limited, one of our key objectives is to study and understand processes occurring in silicon-based cells using in-situ and/or operando techniques (differential electrochemical mass spectrometry, electrochemical atomic force microscopy etc.) to direct materials development. 

Figure 1: Schematic view of the setup used for electrochemical atomic force microscopy of practical silicon anodes.

Active and Inactive Materials Design

One of the main disadvantages of silicon as active material is the pulverization effect which, however, can be mitigated by using nanoscale particles. Thus, the research at BELLA is dedicated in part to the synthesis of advanced nanomaterials and composites with different morphologies by chemical and physical methods. Besides, we explore new cell components such 3D current collectors, polymer binders, electrolytes, to name a few, to tailor the interplay between the active and inactive electrode materials. 

Figure 2: Photograph of a three-dimensional copper current collector for silicon anodes. The microwire network was produced by technical embroidery.