Multiwalled-carbon-nanotubes (MWCNTs) are studied as a conductive additive for all-solid-state lithium-ion batteries using a silicon nanoparticle electrode. Lithium batteries with nanosilicon (n-Si) electrodes and MWCNTs demonstrate nearly a 100% increase in long-term specific capacity over comparable batteries that instead employ acetylene black. For over 100 cycles, reversible capacities over 900 mAh g(-1) are measured for these n-Si/MWCNT electrodes. MWCNTs are shown to be a superior conducting additive for Li batteries with a solid-state construction, and Si nanoparticles are shown to demonstrate improved reversible cycling over bulk Si anode material. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3479551] All rights reserved.