Significant advances in both energy density and rate capability for Li-ion batteries are necessary for implementation in electric vehicles.  We have employed two different methods to improve the rate capability of high capacity electrodes.   For example, we previously demonstrated that thin film high volume expansion MoO3 nanoparticle electrodes (~2 �m thick) have a stable capacity of ~630 mAh/g, at C/2 (charge/dicharge in 2 hours).  By fabricating thicker conventional electrodes, an improved reversible capacity of ~1000 mAh/g is achieved, but the rate capability decreases. To achieve high-rate capability, we applied a thin Al2O3 atomic layer deposition coating to enable the high volume expansion and prevent mechanical degradation. Also, we recently reported that a thin ALD Al2O3 coating can enable natural graphite (NG) electrodes to exhibit remarkably durable cycling at 50�C. Additionally, Al2O3 ALD films with a thickness of 2 to 4 � have been shown to allow LiCoO2 to exhibit 89% capacity retention after 120 charge�discharge cycles performed up to 4.5 V vs. Li/Li+. Capacity fade at this high voltage is generally caused by oxidative decomposition of the electrolyte or cobalt dissolution. We have recently fabricated full cells of NG and LiCoO2 and coated both electrodes, one or the other electrode as well as neither electrode.  In creating these full cells, we observed some surprising results that lead us to obtain a greater understanding of the ALD coatings. In a different approach we have employed carbon single-wall nanotubes (SWNTs) to synthesize binder-free, high-rate capability electrodes, with 95 wt.% active materials. In one case, Fe3O4 nanorods are employed as the active storage anode material. Recently, we have also employed this method to demonstrate improved conductivity and highly improved rate capability for a LiNi0.4Mn0.4Co0.2O2 cathode material. Raman spectroscopy was employed to understand how the SWNTs function as a highly flexible conductive additive.

High rate and high capacity Li-ion electrodes for vehicular applications

243rd National Meeting (2012)

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