Authors: Motoki Horibe | Naoto Tanihata | Hayami Takeda | Masanobu Nakayama
Source: ECS Meeting Abstracts (article, 2024-11-22)
Field: Chemistry — Electrochemistry

Universal Neural Network Potential Driven Molecular Dynamics Study of CO<sub>2</sub> and O<sub>2</sub> Evolution at the Ethylene-Carbonate/Charged-Electrode Interface Lithium-ion batteries are currently used in large power sources such as automobiles, for which durability and safety are required. However, LIB suffers from degradation such as CO 2 generation from electrolyte decomposition and O 2 emission from cathode materials. These side reactions and gas generation can cause serious problems leading to ignition and explosion. It is important to understand how reactions occur at the interface during charging to generate CO 2 and O 2 . This reaction at the cathode/electrolyte interface has been studied by various experimental and computational methods. In particular, density functional theory (DFT) simulation studies are effective in clarifying the decomposition process of the electrolyte at the atomic level. However, DFT calculations for liquid electrolytes are computationally demanding, since the number of molecules are prone to be large when considering molecule-molecule interaction 1 . To solve, we apply universal neural network potential (UNNP) molecular dynamics (MD) simulations to the reaction at the electrolyte solution / solid electrode interface. In this study, we focused on Li x CoO 2 (0≤x≤1) and Li x NiO 2 (0≤x≤1) as cathode materials, and ethylene carbonate (EC) as the electrolyte solvent. The model consists of Li 180(1-x) Ni 180 O 360 (Li 180(1-x) Co 180 O 360 ) slab and 100 EC molecules. After the structural relaxation calculations, MD calculations were performed for a 500 ps in a canonical (NVT) ensemble with a time step of 1 fs. Temperatures were 373 K and 473 K, which are below the boiling point of EC. In LiCoO 2 , no decomposition of the electrode or electrolyte was observed. On the other hand, CO 2 was generated in the MD calculation for LiNiO 2 . The generation process (3 steps) is shown below. (1) Hydrogen dissociation/desorption from EC molecules. (2) Combination of the ethylene group carbon of the EC molecule, from which hydrogen dissociation has occurred, with the oxygen on the cathode surface. (3) Ring-opening between the ethylene group carbon of the EC molecule and oxygen, resulting in CO 2 generation. The O 2 generation phenomenon was observed to occur in the following three steps as shown in Figure 1. (1) Ni moves to the Li layer to form NiO 4 tetrahedron. (Figure 1 (a) → (b)) (2) Oxygen dimer is formed by the bonding of NiO 4 tetrahedron and NiO 5 polyhedron derived from NiO 6 octahedron. (Figure 1 (c)) (3) Oxygen dimer is released. (Figure 1 (d)) Technical details will be presented, in particular on CO 2 evolution, at the poster session. References 1. Okuno et al. The Journal of Physical Chemistry C 2019 123 (4) Figure 1 Ethylene carbonate ; Carbonate ; Electrode ; Interface (matter) ; Ethylene ; Chemical physics ; Molecular dynamics ; Materials science ; Artificial neural network ; Chemical engineering ; Nanotechnology ; Chemistry ; Physical chemistry ; Computational chemistry ; Computer science ; Electrolyte ; Organic chemistry ; Adsorption ; Catalysis ; Engineering ; Artificial intelligence ; Metallurgy Electrochemical Analysis and Applications ; Advanced Chemical Sensor Technologies ; Gas Sensing Nanomaterials and Sensors