Atomistic Dynamics Investigation of the Thermomechanical Properties and Li Diffusion Kinetics in psi-Graphene for LIB Anode Material
S Thomas and EB Nam and SU Lee, ACS APPLIED MATERIALS & INTERFACES, 10, 36240-36248 (2018).
A fundamental understanding of the thermomechanical properties of electrode materials and Li-ion diffusion kinetics is indispensable for designing high-performante Li-ion batteries (LIBs) with high structural stability and safety. Herein, we performed both molecular dynamics (MD) simulations and density functional theory (DFT) calculations to investigate the thermomechanical properties and Li diffusion kinetics in a two-dimensional (2D) defect-filled graphene-like membrane consisting of 5-, 6-, and 7-membered rings, called psi (psi)-graphene. Our results reveal that psi-graphene has a negative linear thermal expansion coefficient, a high specific heat capacity, and high elastic constants that satisfy the Born's criterion for mechanical stability, which can be elucidated as the evidence of strong anharmonicity in psi-graphene because of the soft out-of-plane bending modes. These characteristics can help prevent the thermal runaway that can occur during overheating and prevent structural damage because of the severe volume expansion of the LIBs. In addition, the Li diffusion coefficient was estimated to be 10(-9) cm(2)/s at 300 K with a low Li migration activation energy (<0.16 eV), which suggests favorable electrode kinetics with fast Li conduction. Our DFT calculations also show that tp-graphene can possess a fairly good theoretical capacity (339 mA h g(-1)) and a lower Li diffusion barrier (<0.21 eV). Our results suggest that the new fundamental insights presented here will help to stimulate further experimental work on psi-graphene for promising future applications as a superior electrode material for LIBs.
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