{"id":5965,"date":"2012-07-18T22:26:45","date_gmt":"2012-07-18T22:26:45","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/?p=5965"},"modified":"2012-07-18T22:26:45","modified_gmt":"2012-07-18T22:26:45","slug":"carbon-nanotubenanofiber-electrodes-for-high-energy-rechargeable-li-o2-batteries","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/carbon-nanotubenanofiber-electrodes-for-high-energy-rechargeable-li-o2-batteries\/","title":{"rendered":"Carbon Nanotube\/Nanofiber Electrodes for High-energy Rechargeable Li-O2 Batteries"},"content":{"rendered":"

Recently, Li-O2<\/sub> batteries have attracted much attention as potential next-generation alternatives to lithium-ion batteries for electric vehicle energy storage [1<\/a>] <\/sup>. This interest is due to the extremely high theoretical energy density (~3200 Wh\/kgLi2O2<\/sub>) available in the Li-O2<\/sub> system. During discharge in a Li-O2<\/sub> cell, Li+<\/sup> reduces molecular O2<\/sub> to form Li2<\/sub>O2<\/sub>in the void volume of a porous cathode [2<\/a>] <\/sup>. Our recent work [3<\/a>] <\/sup> has demonstrated that arrays of aligned carbon nanofiber electrodes with extremely high void volume (>90%) can deliver gravimetric energy densities ~5 times higher than state-of-the-art Li-ion batteries at comparable rates, as evident in Figure 1. The reported energy density approaches the theoretical energy density for Li2<\/sub>O2<\/sub>. The aligned carbon nanofiber structures from our previous study [3<\/a>] <\/sup> were fabricated directly on a porous alumina substrate using chemical vapor deposition [4<\/a>] <\/sup> [5<\/a>] <\/sup>. Aligned nanofiber\/nanotube structures also provide an ideal platform for performing ex-situ studies of the morphological evolution of Li2<\/sub>O2<\/sub>, and the shapes of Li2<\/sub>O2<\/sub> discharge products have been shown to resemble toroids [2<\/a>] <\/sup> [3<\/a>] <\/sup> at low rates, as Figure 2 shows. Recent work has focused on the fabrication of tall (~500 <\/ins>\u00b5m- <\/ins>thick) freestanding vertically aligned carbon nanotube (VACNT) carpets as binder-free electrodes for the Li-O2<\/sub> system. Additionally, we have performed extensive ex-situ SEM and TEM studies to investigate the morphological evolution of Li2<\/sub>O2<\/sub> upon discharge and charge.<\/p>\n\n\t\t