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Simulating Mechanical Deformation in Nanomaterials with Application for Energy Storage in Nanoporous Architectures

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posted on 27.10.2009, 00:00 by Thi X. T. Sayle, Phuti E. Ngoepe, Dean C. Sayle
Central to porous nanomaterials, with applications spanning catalysts to fuel cells is their (perceived) “fragile” structure, which must remain structurally intact during application lifespan. Here, we use atomistic simulation to explore the mechanical strength of a porous nanomaterial as a first step to characterizing the structural durability of nanoporous materials. In particular, we simulate the mechanical deformation of mesoporous Li−MnO2 under stress using molecular dynamics simulation. Specifically, such rechargeable Li-ion battery materials suffer volume changes during charge/discharge cycles as Li ions are repeatedly inserted and extracted from the host β-MnO2 causing failure as a result of localized stress. However, mesoporous β-MnO2 does not suffer structural collapse during cycling. To explain this behavior, we generate a full atomistic model of mesoporous β-MnO2 and simulate localized stress associated with charge/discharge cycles. We calculate that mesoporous β-MnO2 undergoes a volume expansion of about 16% when Li is fully intercalated, which can only be sustained without structural collapse, if the nanoarchitecture is symmetrically porous, enabling elastic deformation during intercalation. Conversely, we predict that unsymmetric materials, such as nanoparticulate β-MnO2, deform plastically, resulting in structural collapse of (Li) storage sites and blocked transport pathways; animations revealing elastic and plastic deformation mechanisms under mechanical load and crystallization of mesoporous Li−MnO2 are presented at the atomistic level.