Structured silicon anodes for lithium battery applications

Pillar arrays fabricated on silicon substrates have been tested as potential anodes for lithium batteries. Electrodes of array characteristics, diameter 580 +/- 150 nm; fractional surface coverage 0.34; height 810 nm are reported here. Cyclic voltammetry (CV) and cyclic galvanostatic tests of alloying/dealloying of electrochemically produced lithium with silicon were carried out, and results correlated with SEM studies. Aerial current densities in the low and fractional mA cm(-2), and voltage 25 mV to 2 V (vs. L/Li+) were used. CV features correspond to various Zintl phase compounds (ZPCs). Structured electrodes of Si pillars maintained their structural integrity throughout cycling; planar Si electrodes showed cracks (2 mum features) after 50 cycles. A model is advanced in which lithium diffuses through a layer of ZPC to react with Si: growing ZPCs plastically deforms where necessary. Upon lithium dealloying vacancies coalesce to form voids at the ZPC/Si interface, Si rejoins the substrate, or precipitates out as a nanocrystalline material, and the voids appear as a fine pattern of cracks, looking like dried mud. The extra surface area that a pillar structure can confer on Si electrodes is essential and makes it practical to consider the possible eventual use of such anodes in integrated battery structures. (C) 2003 The Electrochemical Society.