Silicon Composite Anodes: Half and Full Cell Studies

Monday, May 12, 2014: 09:00
Bonnet Creek Ballroom I, Lobby Level (Hilton Orlando Bonnet Creek)
M. Karulkar (Ford Motor Company)
With the demand for electric vehicles increasing, the need for higher energy and power density in automotive batteries is apparent. Silicon-carbon composites represent promising anode materials, striking a balance between the stability of graphite and the high capacity of pure silicon. However, cycle life and current density remain too low when considering practical applications and real-world automotive targets. 

C-Si anodes are typically examined in half-cell applications, being cycled against a lithium counterelectrode. However, Li is a poor metal for cycling, and has the potential to confound cycle life data as mossy Li grows and increases cell impedance. Figure 1 shows the results of Li-Li cycling, and indicates approximately linear relationships between percent lithium lost and cycle life. To get a more straightforward assessment of C-Si anodes, full cell testing has been performed, and compared to half-cell cycling against lithium. Cycle life, capacity, and other performance metrics will be examined.

Several innovations have been demonstrated to improve C-Si anode performance.[1] The Capacity Control Method has been demonstrated as an effective means to improve cycle life and current density (Figure 2).  Additionally, the Conductive Dual Cast technique has been shown to improve capacity (Figure 3). Both of these techniques have been more thoroughly explored in the present work, and a relationship between capacity cutoff, current density, and cycle life has been established.

Deviations from the Si-C half-cell ideal are examined in the context of energy and power density. For instance, the effect of pairing high-capacity C-Si with lower-capacity intercalation cathodes is investigated using modeling and the full-cell testing from above. The costs and benefits of conductive layers, which add thickness and weight to the anode, are discussed. Finally, the effect of Capacity Control method, which by design underutilizes C-Si anodes, is analyzed in relation to real-world automotive targets.

[1] M. Karulkar, R. Blaser, R. Kudla, Electrochemical Society 224th Meeting, San Francisco, Abstract 227 (2013).