Improving Rate Capability in High-Energy Thick Lithium-Ion Batteries through Graded and Structured Electrodes

Next-generation electric vehicles (EVs) made with Lithium-ion batteries (LIBs) require both higher energy density and higher power density to reach $80/kWh at a 300-mile range as laid out by the US Department of Energy.¹ LIBs made with Nickel-rich layered oxide cathodes and graphite anodes can maintain energy densities around 250 – 300 Wh/kg at low charge and discharge rates.^2,3 However, due to slow ion transport encountered with increasingly thick electrodes, these LIBs exhibit poor rate capability, with more than 50% capacity loss experienced at 4C and higher charge/discharge rates.⁴ Graded electrodes (GEs) are one approach that have been proposed to improve the efficiency of lithiation in thick electrodes. GEs assemble two or more electrode layers with differing porosity values into a single thick electrode. In addition to GEs, structured electrodes (SEs) are another means to enhance transport in thick electrodes by re-distributing electrode materials on a micron-scale into line- and grid-pattern electrode architectures. The controlled electrode architecture introduced by SEs reduces the effective electrode tortuosity and enables better electrolyte infiltration in thick battery electrodes.^5,6<br/>Our research aims to uncover new SE and GE electrode designs for EV batteries. In this study we explored the individual and combined benefits of SEs and GEs for improving the rate capability of high-energy LIBs through computational modeling in VIBE,^7,8 a suite of multi-scale and multi-physics battery modeling tools developed by Oak Ridge National Laboratory. A three-dimensional physics-based continuum-scale electrochemical model was used in VIBE to model a series of electrode designs for a comparative electrode design analysis, including conventional electrodes, GEs, SEs, and combined SE and GE geometries. A LiNi_0.6Mn_0.2Co_0.2O₂ cathode and graphite anode are used as model material systems due to their current relevance for EVs. To ensure a consistent analysis, the active material loading is held constant for all models to allow us to study the effect of mass distribution and electrode design on LIB rate capability. Our current results show that at high discharge rates of 2C, 4C, and 6C, SE LIBs demonstrate a 33 – 37 % improvement in energy density, and the combined SE and GE LIB electrode designs demonstrate a 46 – 67% improvement in energy density over conventional cells. This study demonstrates the advantage of implementing SEs and GEs for thick electrode LIBs with improved rate capability. These results affirm the need to purse new manufacturing approaches that enable SE and GE electrode designs to enhance the performance of existing LIB materials.<br/><br/>References<br/>1. Energy Storage Grand Challenge Roadmap, <i>Energy.gov</i> (2020) https://www.energy.gov/energy-storage-grand-challenge/articles/energy-storage-grand-challenge-roadmap.<br/>2. C. Heubner et al., <i>Journal of Power Sources</i>, 419, 119–126 (2019).<br/>3. T. Placke, R. Kloepsch, S. Dühnen, and M. Winter, <i>J Solid State Electrochem</i>, 21, 1939–1964 (2017).<br/>4. L. Kraft, J. B. Habedank, A. Frank, A. Rheinfeld, and A. Jossen, <i>J. Electrochem. Soc.</i>, 167, 013506 (2019).<br/>5. K.-H. Chen et al., <i>Journal of Power Sources</i>, 471, 228475 (2020).<br/>6. C. L. Cobb and S. E. Solberg, <i>J. Electrochem. Soc.</i>, 164, A1339–A1341 (2017).<br/>7. S. Allu et al., <i>Journal of Power Sources</i>, 325, 42–50 (2016).<br/>8. S. Allu et al., <i>Journal of Power Sources</i>, 246, 876–886 (2014).<br/><br/>Acknowledgement<br/>This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Materials and Manufacturing Technologies Office, Award Number DE-EE0010226. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.