Here we describe a model for lithium titanate spinet paired with an activated carbon electrode: an asymmetric hybrid supercapacitor. The model is compared to experimental results. The performance of this system is compared to a lithium titanate spinel/lithium iron phosphate battery. The model is used to study the, performance of these chemistries and to assist in cell optimization. A Ragone plot is generated for various cell designs in order to assess the ability of the chemistries to achieve the U.S. Department of Energy goals for hybrid-electric vehicles. The specific energy of a cell is maximized by optimizing the design for a fixed time of discharge. The thickness and porosity of both electrodes are varied, while holding constant the capacity ratio for the, two electrodes, as well as the properties of the separator. The capacity ratio can also be optimized for each time of discharge. A 41% increase in specific power is seen when one optimizes the capacity ratio of a lithium titanate spinel/iron phosphate battery. The optimized designs derived here can be used as a starting point for battery manufacturers and to help decrease the time to commercialization. (C) 2008 The Electrochemical Society.