Lithium ion batteries (LIBs) have been a subject of an intense research since their first commercialization more than 25 years ago. The development of high capacity electrode materials is the most critical limiting factor to progress to the next generation batteries for electric vehicles. In the case of anode material, silicon has the highest theoretical capacity (3579 mAh/g), which is ten times more than the capacity of the state-of-the-art material graphite (370 mAh/g). However, silicon anodes experience dramatic volume change during lithiation and delithiation of more than 300 %, which leads to pulverization of anode material, unstable solid electrolyte interface formation and subsequent battery failure. In order to solve these problems, nanostructured anode materials
(e.g. nanoparticles, porous nanoparticles, nanowires, double-walled nanotubes) have been extensively studied.
The NaMLab gGmbH is focusing on these challenges by developing new high capacity anode structures using Si nanowires as anode material (Fig. 1) and integrating those with the help from strong partners in research and industry into novel LIBs. The Si nanowires are subsequently coated with a highly conductive pyrolytic carbon coating (Fig. 2) established at NaMLab to improve the chemical and mechanical stability while ensuring a continuous electrical contact to the carbon current collector during long-term cycling. A stable operation of carbon coated Si nanowires in a LIB with a high capacity of 4 mAh/cm2 at high charge/discharge rates for more than 600 cycles has been demonstrated. As the capacity per weight is the most important criteria for batteries targeting automotive applications, the binder-free high capacity Si nanowire anodes directly grown on a light-weight carbon based current collector give a unique opportunity for ongoing studies related to the integration in cell designs for batteries, which are relevant for application.
Furthermore, NaMLab is developing an in situ-Characterization of the solid electrolyte interface at the Si anode by employing Raman-Spectroscopy. This is a non-destructive way to determine the components of the anode, the electrolyte and their interface. It allows the monitoring of compositional and structural changes during the charging and discharging processes. Thus, the mechanisms of degradation can be investigated in real-time (Fig.3).
The strong collaboration with our partners Fraunhofer IWS, IKTS, the Leibniz institute IFW and the TU Dresden within the framework of the projects “BaMoSa” and “KaSiLi” yielded full cells with Si nanowire anodes involving Li-Ion and Li-sulfur chemistry up to the pouch cell level.
Dr. Matthias Grube
Fraunhofer IWS, Dresden (Germany), Fraunhofer IKTS, Dresden (Germany), Fraunhofer IFAM, Dresden (Germany), Leibniz-Institute IFW, Dresden (Germany), Leibniz-Insitute IPF, Dresden (Germany), TU Dresden (IAC, IfWW, IOF), Dresden (Germany)