Insights on the Structural Changes and Mechanical Properties of Lithiated Li1+XMn2O4 Nanoporous Structures, Where 0 ≤ x ≤ 1 for Li-Ion Battery Cathodes

Abstract

Most cathode materials for Li-ion batteries suffer from severe specific capacity due to structural changes that occur during the process of cycling, which may lead to fractures. Nanoporous structured materials can act as a host lattice to accommodate Li during the processes of intercalation and de-intercalation for the application of Li-ion batteries. These materials have large surface areas and volume density which allows them to flex within their pores during cycling. Herein, molecular dynamics simulations were used to study the structural changes and mechanical properties of lithiated Li1+xMn2O4 nanoporous structures to bring insights into the development of newer applications for Li-ion batteries. The DL_POLY code under the NST ensemble was employed to recrystallize three nanoporous structures, with different lattice sizes i.e. 75 Å, 69 Å and 67 Å and varying Li concentrations. The structures evolved into single and multiple grains during the recrystallization process. The microstructures harvested from the structures resulted in defective spinel and layered components. The pores of the structures changed in size with increasing Li concentration, where they either reduce, increase or close up; this was also accompanied by volume change in materials. Consequently, the nanoporous 69 Å was observed to have better resistance to volume change at Li1.75Mn2O4 concentration which rendered its counterparts evolving into multi-grained structures and experiencing great expansion. Furthermore, at this concentration, nanoporous 69 Å showed robust properties in terms of its yield strength of 9.65 GPa, compared to nanoporous 75 Å with 2.77 GPa and 67 Å with 6.84 GPa. Nanoporous 69 Å is, therefore, more resilient to structural changes, which imply that it can better withstand harsh conditions that may lead into the cathode to fracture.