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Nanoelectrodes for Li Batteries

Fig. 1
Fig. 1: Scanning electron microscopy (SEM) image of electrode assembly composed of Si-nanowires grown by CVD on 3D structured carbon meshes.

Lithium ion batteries (LIBs) have been subject of an intense re-search since their first commercialization more than 25 years ago. In a path to create a full electric car comparable to gasoline-powered vehicles, LIBs continue to be the most advanced and the most promising option. The development of high capacity electrode materials is the most critical limiting factor to the progress of 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 currently used 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 interphase 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.

Fig. 2
Fig. 2: SEM image of a Si nanowire coated with an extremely uniform pyrolytic carbon layer for SEI control and electric conductivity enhancement.

 

 

 

NaMLab gGmbH is focusing on these challenges by developing new high capacity anode assemblies using Si nanowires as anode material (Fig. 1) and integrating those with the help of partners in research and industry into novel full cell LIBs. The Si nanowire anode assemblies are subsequently coated with a highly conductive pyrolytic carbon coating (Fig. 2) previously 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 achieved (Fig. 3). 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 assembly studies and study of properties in application relevant battery cell designs.

Fig. 3
Fig. 3: Long-term cycling test of carbon coated Si nanowires at a high charge/discharge current of
2.1 A/g(Si) in a half-cell setup.

 

 

The strong collaboration with our partners Fraunhofer IWS, IKTS, IFAM as well as with the Leibniz institute IFW and the TU Dresden within the framework of the BMBF wing center “BamoSa” has been intensified to construct full-cells made of the Si nanowire anodes involving Li-Ion and Li-sulfur chemistry. Previously prepared Si nanowires anodes integrated in 3rd generation Li-S batteries exhibited a specific energy of approximately 400 Wh/kg. Currently, the integration of large scale Si nanowire electrodes in LIB pouch cells is successfully established.

 

Contact: Dr. Walter M. Weber

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01187 Dresden
Germany 

Phone: +49.351.21.24.990-00
Fax: +49.351.475.83.900

info (at) namlab.com

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