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ion High-Power Li-Ion Anode Materials

Rishi Raj, University of Colorado at Boulder, DMR 0907108

• Amorphous silicon oxycarbide (SiCO) ceramics made from siloxane-based polymers can be discharged in a fraction of a second without failure (Fig. 1).

• These anodes have the potential to deliver nearly 100kWkg–1 at an energy density of 100Whkg–1. A start-up PDC Energy, LLC, launched in 2009, operated for one year. Discussions with Toray Carbon are ongoing.

• The mechanism is the sequestration of Li atoms at mixed bond Si-C-O tetrahedra at interfaces with graphene created by an in-situ process (Fig. 2). These materials are called polymer-derived-ceramics (PDCs).

• The caveat: SiCO embodies a large hysteresis (~0.75V) which must be overcome for viability. (Ahn and Raj, doi:10.1016/j.jpowsour.2009.12.116)

• Currently the fundamental mechanism of the hysteresis is being investigated under the postulate that the strain induced by Li insertion modifies the energy levels for their placement (Fig. 2).

Fig. 1: The red plot shows the capacity (mAhg–1) as the charging rate, shown in green increases; C-rate implies number of charge cycles per hour. The absence of damage to the anode is shown by full recovery. (Ahn and Raj: doi:10.1016/j.jpowsour.2010.09.086)

Fig. 2: PDCs are interface materials, expected to contain graphene like networks of carbon that form the “interface” to which mixed bond of Si-C-O as shown above, are anchored (DOI: 10.1111/j.1551-2916.2006.00920.x). The Li atoms segregate to these tetrahedra at concentrations of 10 to 100 times greater than in elemental graphite (DOI: 10.1111/j.1551-2916.2009.03539.x).