“First-principles sampling simulation approaches to battery science and technology”

The 1st R-CCS International Symposium 18 Feb,2019
"First-principles sampling simulation approaches to battery science and technology"

Development of next-generation battery is a most important issue in modern society. For emerging technologies such as electric vehicle and smart grid, batteries with higher energy and power densities, higher safety and longer durability are needed. From the viewpoint of materials science, elucidation of all electronics and atomic processes in the battery is essential. However, the in-situ experimental observations are still difficult and many problems remain unsolved. Then, we have addressed understanding the battery microscopic mechanisms by means of first-principles sampling simulation approaches based on density functional theory (DFT) calculations of the electronic states with reasonable accuracy. By adding the multiple parallelisation functions to a DFT molecular dynamics (MD) open source “CPMD” [1], we constructed “stat-CPMD extension” for efficient sampling and free energy profile calculation of chemical and redox reactions on the K computer. The stat-CPMD code showed FLOPS efficiency over 30% and SIMD ratio over 70% in the best cases. We then addressed long-standing issues of the SEI (solid electrolyte interphase) formation and properties at anode – organic electrolyte interfaces, which really determines the performance and the reliability of the battery. Besides, we have investigated the electrochemical and transport properties of a new class of electrolyte, “highly-concentrated electrolyte”, emerging recently. Regarding the SEI issue, we found a novel mechanism of the VC additive effect on the initial reductive decomposition of EC solvent [2], and then proposed a probable subsequent mechanism with the decomposed products toward the SEI formation at the electrode – electrolyte interface [3,4], which overturns the conventional understandings. For the latter, we elucidated origins of the unusual electrochemical stability and excellent ion transport in superconcentrated electrolytes [5-9]. These findings via DFT sampling simulations provide new perspectives for the battery science and technology. These works were done in collaboration with Dr. Keitaro Sodeyama (NIMS), Dr. Yukihiro Okuno and Keisuke Ushirogata (FUJIFILM corporation), Prof. Yuki Yamada and Prof. Atsuo Yamada (The University of Tokyo), and partly supported by MEXT as “Priority Issue (No. 5) on Post K computer” (Development of new fundamental technologies for high-efficiency energy creation, conversion/storage and use).

Yoshitaka Tateyama
(National Institute for Materials Science(NIMS))