Researchers worldwide view the high theoretical specific energy of the lithium-air or lithium-oxygen battery as a promising path to a transformational energy-storage system for electric vehicles. Here, we present a self-consistent material-to-system analysis of the best-case mass, volume, and cost values for the nonaqueous lithium-oxygen battery and compare them with current and advanced lithium-based batteries using metal-oxide positive electrodes. Surprisingly, despite their high theoretical specific energy, lithium-oxygen systems were projected to achieve parity with other candidate chemistries as a result of the requirement to deliver and purify or to enclose the gaseous oxygen reactant. The theoretical specific energy, which leads to predictions of an order of magnitude improvement over a traditional lithium-ion battery, is shown to be an inadequate predictor of systems-level cost, volume, and mass. This analysis reveals the importance of system-level considerations and identifies the reversible lithium-metal negative electrode as a common, critical high-risk technology needed for batteries to reach long-term automotive objectives. Additionally, advanced lithium-ion technology was found to be a moderate risk pathway to achieve the majority of volume and cost reductions. Broader contextThe commercialization of battery electric vehicles has provided a glimpse of one potential future paradigm of the transportation sector. Moving to an electricitybased transportation system could enable a domestically produced, potentially near-zero emission energy source if coupled to clean, domestic sources of electricity production. However, the batteries used in electric vehicles in 2013 are too expensive, large, and heavy for mass market adoption; signicant progress is needed. The lithium-air or lithium-oxygen battery is a high visibility archetype for the "best-case" possible electrochemical energy-storage system for electric vehicles. We present a material-to-systems analysis of the lithium-oxygen chemistry with comparison to current and future lithium-based chemistries to identify scientic challenges and technological possibilities. Through translation of materials-level science to the systems-level engineering, we show that a lithiumoxygen battery system for automotive applications has comparable cost, volume, and mass to other advanced chemistries that are in more mature states of development and have less technical risk. This result demonstrates that system-level analysis is necessary and may contradict trends predicted from active materials based specic energy and energy density calculations that are the basis for many research investment decisions.

A materials-to-system analysis for the lithium-sulfur (Li-S) electric vehicle battery is presented that identifies the key electrode and cell design considerations from reports of materials chemistry. The resulting systems-level energy density, specific energy and battery price as a function of these parameters is projected. Excess lithium metal amount at the anode and useable specific capacity, electrolyte volume fraction, sulfur to carbon ratio and reaction kinetics at the cathode are all shown to be critical for the high energy density and low cost requirements. Electrode loading is determined as a key parameter to relate the battery price for useable energy to the investigated design considerations. The presented analysis proposes that electrode loadings higher than 8 mAh/cm 2 (∼7 mg S/cm 2 ) are necessary for Li-S systems to exhibit the high energy density and low cost required for transportation applications. Stabilizing the interface of lithium metal at the required current densities and areal capacities while simultaneously maintaining cell capacity with high sulfur loading in an electrolyte starved cathode are identified as the key barriers for ongoing research and development efforts to address. In the search for high energy density and inexpensive rechargeable batteries for the electric vehicles, Li-S batteries have gained significant attention due to the high specific capacity (1675 mAh/g), low cost, natural abundance and non-toxicity of elemental sulfur.1-6 Compared to the state-of-art Li-ion batteries, Li-S batteries have very high theoretical specific energy of 2567 Wh/kg.1-6 The Li-S battery is commonly composed of a sulfur-carbon composite cathode, an organic electrolyte and a lithium anode.1-6 The overall Li-S redox reaction is given in equation 1.with a standard potential of U 0 = 2.2 V (vs Li/Li + ). 1,2Despite these attractive features of the Li-S battery, multiple formidable challenges limit the cycle life significantly. [1][2][3][4][5][6] Firstly, precipitation of insulating reactants, sulfur and Li 2 S, in the cathode leads to poor electronic conductivity and passivation that could limit the active material utilization.1-6 Secondly, the soluble polysulfide reaction intermediates produced during charging can migrate to the anode where they react with Li to either precipitate on the anode surface or migrate back to the cathode causing infinite charging.1-6 This polysulfide shuttle mechanism leads to poor coulombic efficiency and significant self-discharge as well as corrosion of the Li-anode.1-6 Finally, the instability of the Li-anode is a major concern.2,4,5,7 Li surface area can increase significantly with cycling due to morphological changes, which accelerate Li and electrolyte depletion owing to the absence of a stable interphase. 2,4,5,7 While polysulfide migration may lead to the corrosion of dendritic or high surface area lithium reducing the risk of short circuiting, the resulting reactions typically result in a reduction in inventory of cyclable lithium. 4 All of these mechanisms ...

Summary A 1D model is developed for the Li‐S cell to predict the effect of critical cathode design parameters—carbon‐to‐sulfur (C/S) and electrolyte‐to‐sulfur (E/S) ratios in the cathode—on the electrochemical performance. Cell voltage at 60% depth of discharge corresponding to the lower voltage plateau is used as a metric for calculating the cell performance. The cathode kinetics in the lower voltage plateau is defined with a single electrochemical reaction; thus, the model has a single apparent kinetic model parameter, the cathode exchange current density (i0,pe). The model predicts that cell voltage increases considerably with increasing carbon content until a C/S ratio of 1 is attained, whereas the enhancement in the cell voltage at higher ratios is less obvious. The model can capture the effect of the C/S ratio on the cathode kinetics by expressing the electrochemically active area in the cathode in carbon volume fraction; the C/S ratio in the cathode does not affect i0,pe in the model. On the other hand, the electrolyte amount has a significant impact on the kinetic model parameter such that increasing electrolyte amount improves the cell voltage as a result of increasing i0,pe. Therefore, in the model, i0,pe needs to be defined as a function of the electrolyte volume fraction, which is known to have a crucial effect on reaction kinetics.

The effect of electrolyte-to-sulfur (E/S) ratio on the electrochemical and cell-and systems-level performance of a Li-S battery is investigated through modeling efforts. A 1-D electrochemical model is proposed predicting the cell voltage at 60% discharge depth. In the model, increasing electrolyte amount improves the cell voltage by linearly increasing the cathode exchange current density, which is the single kinetic model parameter. Moreover, cathode specific capacity is either defined as a linear function of the E/S ratio or taken constant in the performance models. Increasing E/S ratio enhances the cell-and systems-level specific energy and energy density until 9 mL/g S when cathode specific capacity depends on the E/S ratio. However, when the cathode specific capacity is constant at 1200 mAh/g S, battery performance decreases continuously with increasing electrolyte amount. The effect of other critical design parameters -cathode thickness, carbon-to-sulfur ratio, S loading and excess Li%-are also considered in the analysis.