Development of a benchmarking model for lithium battery electrodes
Introduction
Lithium Ion Batteries (LIBs) are of special interest with respect to fuel cell battery hybrid systems for light traction (0.5–5 kW) and individual transport (5–200 kW), as well as for battery electric vehicles (BEVs) and stationary applications [1], [2], [3]. The batteries in these systems must fulfill multiple requirements. An increased volumetric EV and gravimetric energy density Em is essential to enabling the achievement of higher operational ranges by BEVs and reducing the mass and volume of fuel cell power trains. The power density Pm of the battery determines the power capability of BEVs and the possible peak load of hybrid fuel cell systems. Increased cyclic and calendaric lifetime, improved safety characteristics, the usage of more abundant raw materials and low specific costs are further important factors for all considered applications. Conventional LIBs must be modified to reach these goals. For this reason, the introduction of novel cell chemistries is required. This paper outlines a benchmarking model that draws on the fundamental material characteristics of lithium battery electrode materials so as to systematically and quantitatively identify their potential for application in different battery and fuel cell hybrid power trains.
Table 1 lists the requirements for the battery in a hybrid electric vehicle (HEV), a BEV and a stationary energy system, as communicated by the Japanese New Energy and Industrial Technology Development Organization (NEDO) [4] and the US Department of Energy (DOE) [5] for the years 2020 and 2030. Additionally, the derived target values for the battery of an in-house, 1 kW direct-methanol fuel cell (DMFC) hybrid system for light traction electric vehicles (LHEVs) are listed [6]. The characteristics of a commercial LIB comprised of a carbon-based anode, a LiNi0.8Co0.15Al0.05O2 cathode and an organic solvent-based electrolyte from Gaia are opposed [6].
Based on the discrepancy of the target values and LIB-characteristics, state-of-the-art systems must be optimized with different prioritizations. Table 1 specifies the respective priorities from 0 for a low priority to ++ for a high priority. BEV batteries place a high demand on volumetric and gravimetric energy density and costs. The power densities of present systems fulfill the demand of BEVs, while the cyclic and calendaric lifetimes must be increased.
In contrast, HEV and LHEV batteries have high priorities in terms of power density and lifetime. The gravimetric energy density of the exemplary LIB has to be increased by 20% and 36% for HEV and LHEV batteries, respectively. The higher value required for LHEVs arises from the lower limits for battery mass and volume in the comparably smaller systems. Due to the high volumetric energy density of conventional batteries, they attain the requirements of the hybrids considered. State-of-the-art LIBs reach the desired energy and power densities needed for stationary applications, while their calendaric and cyclic lifetime, as well as their costs, must be significantly optimized. According to the derived prioritization for the additional parameters of raw materials and safety, all applications must fulfill high safety standards, whereas the utilized resources are more important for large-scale BEV and stationary batteries.
Section snippets
Development of a benchmarking model
In order to evaluate electrode materials for the deployment in HEVs, BEVs and stationary applications, a benchmarking system originally developed by Camp et al. is applied [7]. The required material characteristics are the following: energy density, power density, safety, lifetime, costs and raw materials, which are defined in the following part to enable quantitative benchmarking. The process is based on the calculation of valuation factors for the different characteristics F(char), which are
Benchmarking of electrode materials
Based on the evaluated material characteristics, evaluation factors are calculated according to Eq. (1). The respective minimum and maximum values (benchmarks) are identified in an extensive literature study, revealing the characteristics of numerous electrode materials.
The exemplary scale of the gravimetric energy density of cathodes F(Em) ranges from 1, for the minimum value of Em = 219 Wh/kg for lithium manganese spinel cathodes (LiMn2O4), up to a total of 10 for the maximum value of Em
Conclusion
The benchmarking model presented in this study enables a systematic selection of electrode materials for lithium batteries in future hybrid fuel cell electric vehicles, battery electric vehicles and stationary systems. Based on the evaluation of accessible material characteristics from the literature, it was possible to implement comparable scales for the quantitative benchmarking of anode and cathode materials. The model considers parameters for energy density, power density, safety, lifetime,
Acknowledgements
We would like to thank Thomas Grube and Christopher Wood for proofreading our work and providing input regarding the requirements of the applications considered.
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2016, Journal of Power SourcesCitation Excerpt :Energy is the lifeblood of modern society and plays important roles in the advancement of human civilization [1–3].