Reaction and Mass Transport Simulation of 3-Dimensional All-Solid-State Lithium-Ion Batteries for the Optimum Structural Design

In order to increase energy density and enhance safety, all-solid-sate lithium-ion batteries have been developed as a storage battery for electric vehicle (EV). However, it is necessary to decrease a mass transfer resistance and a reaction resistance because its power density is too low to be applied for EV. In recent years, 3-dimensional (3D) electrode such as an interdigitated electrode is proposed, which can increase power density without losing high energy density ^{[1, 2]}. The purpose of this study is to simulate the electrochemical reaction and lithium-ion transport phenomena of 3D all-solid-state batteries for the optimum design of 3D structure which can fully charge within 5 minutes.

Based on the porous electrode theory, reaction and mass transport at the galvanostatic discharge were simulated ^{[3, 4]}. In this work, the solid-solid interface resistance and the volume change of active materials were neglected. The temperature distribution in the cell was presumed to be uniform. Assuming that active materials are nano-scale particles, lithium diffuses rapidly enough in an active material particle. Therefore, the lithium concentration distribution in the particles was also supposed to be uniform. Figure 1shows some examples of 2D and 3D structures for simulation. These structures are symmetry and the cell is the same size in all structures. In addition, all volume of cathode, solid electrolyte (SE) and anode layer is equal. LiCoO2 and graphite were employed as cathode and anode active materials, respectively. Each structure was simulated at a rate of 1-10C and an SE ionic conductivity of 1-0.01 S/m. And discharge properties of 2D and 3D structures were investigated.

Figure 2shows the galvanostatic discharge curve obtained from the simulation at a rate of 10C and an ionic conductivity of 1 S/m. There was no big difference between the discharge curves of Str.1-13 at a rate of 1C. However, discharge properties of some structures at 10C were degraded because a voltage drop occurred before depth of discharge reaches 1.0. As shown in Figure 2, Str.2 and Str.3 displayed high discharge property at 10C as well as at 1C. This result indicates that discharge property was improved by complicating 3D structures. Furthermore, a cell design parameter was proposed and investigated for the optimum structural design.

References

[1] R.W. Hart, H. White, B. Dunn, D. Rolison, Electrochem. Commun. 5 (2003), 120-123.

[2] Y. Suzuki, H. Munakata, K. Kajihara, K. Kanamura, Y. Sato, K. Yamamoto, T. Yoshida, ECS Transactions, 16 (26) (2009), 37-43.

[3] M. Doyle, T. F. Fuller, J. Newman, J. Electrochem. Soc., 140(1993), 1526-1533.

[4] G. M. Goldin, A. M. Colclasure, A. H. Wiedemann, R. J. Kee, Electrochimica Acta, 64 (2012), 118-129.